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 $188.29   4.764%   $197.2601   $197.26   $197.25   $197.30  
  Purchase #2 $37.44   7.641%   $40.3008   $40.30   $40.30   $40.30  
  Purchase #3 $95.43   9.578%   $104.5703   $104.57   $104.55   $104.60  
  Purchase #4 $185.40   11.251%   $206.2594   $206.26   $206.25   $206.30  
  Purchase #5 $10.72   4.630%   $11.2163   $11.22   $11.20   $11.20  
  Purchase #6 $184.30   9.480%   $201.7716   $201.77   $201.75   $201.80  
  Purchase #7 $194.35   5.487%   $205.014   $205.01   $205.00   $205.00  
  7 purchase totals = $895.93       $966.3925   $966.39   $966.30   $966.50