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 $187.57   9.477%   $205.346   $205.35   $205.35   $205.30  
  Purchase #2 $41.95   8.871%   $45.6714   $45.67   $45.65   $45.70  
  Purchase #3 $17.86   5.842%   $18.9034   $18.90   $18.90   $18.90  
  Purchase #4 $33.30   12.824%   $37.5704   $37.57   $37.55   $37.60  
  Purchase #5 $86.30   6.507%   $91.9155   $91.92   $91.90   $91.90  
  Purchase #6 $232.33   9.421%   $254.2178   $254.22   $254.20   $254.20  
  Purchase #7 $231.75   12.585%   $260.9157   $260.92   $260.90   $260.90  
  7 purchase totals = $831.06       $914.5402   $914.55   $914.45   $914.50