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 $41.93   13.199%   $47.4643   $47.46   $47.45   $47.50  
  Purchase #2 $71.93   8.334%   $77.9246   $77.92   $77.90   $77.90  
  Purchase #3 $208.66   5.398%   $219.9235   $219.92   $219.90   $219.90  
  Purchase #4 $18.95   5.435%   $19.9799   $19.98   $20.00   $20.00  
  Purchase #5 $168.60   11.293%   $187.64   $187.64   $187.65   $187.60  
  Purchase #6 $90.90   9.760%   $99.7718   $99.77   $99.75   $99.80  
  Purchase #7 $123.72   7.501%   $133.0002   $133.00   $133.00   $133.00  
  7 purchase totals = $724.69       $785.7043   $785.69   $785.65   $785.70