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 $160.66   6.611%   $171.2812   $171.28   $171.30   $171.30  
  Purchase #2 $213.94   11.799%   $239.1828   $239.18   $239.20   $239.20  
  Purchase #3 $149.78   9.329%   $163.753   $163.75   $163.75   $163.80  
  Purchase #4 $84.55   11.596%   $94.3544   $94.35   $94.35   $94.40  
  Purchase #5 $59.80   12.235%   $67.1165   $67.12   $67.10   $67.10  
  Purchase #6 $216.61   12.813%   $244.3642   $244.36   $244.35   $244.40  
  Purchase #7 $31.75   5.426%   $33.4728   $33.47   $33.45   $33.50  
  7 purchase totals = $917.09       $1,013.5249   $1,013.51   $1,013.50   $1,013.70