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 $226.37   6.523%   $241.1361   $241.14   $241.15   $241.10  
  Purchase #2 $101.79   8.850%   $110.7984   $110.80   $110.80   $110.80  
  Purchase #3 $55.91   7.826%   $60.2855   $60.29   $60.30   $60.30  
  Purchase #4 $178.73   3.389%   $184.7872   $184.79   $184.80   $184.80  
  Purchase #5 $48.72   7.440%   $52.3448   $52.34   $52.35   $52.30  
  Purchase #6 $201.82   12.190%   $226.4219   $226.42   $226.40   $226.40  
  Purchase #7 $135.47   4.676%   $141.8046   $141.80   $141.80   $141.80  
  7 purchase totals = $948.81       $1,017.5785   $1,017.58   $1,017.60   $1,017.50