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 $207.52   10.710%   $229.7454   $229.75   $229.75   $229.70  
  Purchase #2 $115.67   13.789%   $131.6197   $131.62   $131.60   $131.60  
  Purchase #3 $232.32   5.409%   $244.8862   $244.89   $244.90   $244.90  
  Purchase #4 $247.90   6.117%   $263.064   $263.06   $263.05   $263.10  
  Purchase #5 $240.26   4.622%   $251.3648   $251.36   $251.35   $251.40  
  Purchase #6 $43.65   7.391%   $46.8762   $46.88   $46.90   $46.90  
  Purchase #7 $45.64   13.340%   $51.7284   $51.73   $51.75   $51.70  
  7 purchase totals = $1,132.96       $1,219.2847   $1,219.29   $1,219.30   $1,219.30