Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $141.76   8.521%   $153.8394   $153.84   $153.85   $153.80  
  Purchase #2 $185.52   6.647%   $197.8515   $197.85   $197.85   $197.90  
  Purchase #3 $159.64   5.658%   $168.6724   $168.67   $168.65   $168.70  
  Purchase #4 $157.73   8.686%   $171.4304   $171.43   $171.45   $171.40  
  Purchase #5 $227.82   8.499%   $247.1824   $247.18   $247.20   $247.20  
  Purchase #6 $126.76   11.559%   $141.4122   $141.41   $141.40   $141.40  
  Purchase #7 $241.35   12.234%   $270.8768   $270.88   $270.90   $270.90  
  7 purchase totals = $1,240.58       $1,351.2651   $1,351.26   $1,351.30   $1,351.30