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 $181.65   8.808%   $197.6497   $197.65   $197.65   $197.60  
  Purchase #2 $21.54   8.386%   $23.3463   $23.35   $23.35   $23.30  
  Purchase #3 $194.99   7.652%   $209.9106   $209.91   $209.90   $209.90  
  Purchase #4 $181.25   11.226%   $201.5971   $201.60   $201.60   $201.60  
  Purchase #5 $139.96   7.821%   $150.9063   $150.91   $150.90   $150.90  
  Purchase #6 $177.44   11.102%   $197.1394   $197.14   $197.15   $197.10  
  Purchase #7 $25.44   5.276%   $26.7822   $26.78   $26.80   $26.80  
  7 purchase totals = $922.27       $1,007.3316   $1,007.34   $1,007.35   $1,007.20