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 $119.48   11.747%   $133.5153   $133.52   $133.50   $133.50  
  Purchase #2 $89.79   8.413%   $97.344   $97.34   $97.35   $97.30  
  Purchase #3 $106.60   7.118%   $114.1878   $114.19   $114.20   $114.20  
  Purchase #4 $233.56   5.612%   $246.6674   $246.67   $246.65   $246.70  
  Purchase #5 $71.27   5.645%   $75.2932   $75.29   $75.30   $75.30  
  Purchase #6 $100.30   9.443%   $109.7713   $109.77   $109.75   $109.80  
  Purchase #7 $227.97   7.677%   $245.4713   $245.47   $245.45   $245.50  
  7 purchase totals = $948.97       $1,022.2503   $1,022.25   $1,022.20   $1,022.30