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 $186.64   8.396%   $202.3103   $202.31   $202.30   $202.30  
  Purchase #2 $226.68   12.632%   $255.3142   $255.31   $255.30   $255.30  
  Purchase #3 $83.96   10.445%   $92.7296   $92.73   $92.75   $92.70  
  Purchase #4 $136.64   10.251%   $150.647   $150.65   $150.65   $150.60  
  Purchase #5 $217.57   8.416%   $235.8807   $235.88   $235.90   $235.90  
  Purchase #6 $217.60   13.394%   $246.7453   $246.75   $246.75   $246.70  
  Purchase #7 $125.69   11.484%   $140.1242   $140.12   $140.10   $140.10  
  7 purchase totals = $1,194.78       $1,323.7513   $1,323.75   $1,323.75   $1,323.60