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 $84.95   3.689%   $88.0838   $88.08   $88.10   $88.10  
  Purchase #2 $203.26   10.317%   $224.2303   $224.23   $224.25   $224.20  
  Purchase #3 $189.93   8.180%   $205.4663   $205.47   $205.45   $205.50  
  Purchase #4 $160.62   5.616%   $169.6404   $169.64   $169.65   $169.60  
  Purchase #5 $138.39   8.348%   $149.9428   $149.94   $149.95   $149.90  
  Purchase #6 $31.26   3.391%   $32.32   $32.32   $32.30   $32.30  
  Purchase #7 $58.75   11.754%   $65.6555   $65.66   $65.65   $65.70  
  7 purchase totals = $867.16       $935.3391   $935.34   $935.35   $935.30