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 $71.57   8.231%   $77.4609   $77.46   $77.45   $77.50  
  Purchase #2 $9.70   13.554%   $11.0147   $11.01   $11.00   $11.00  
  Purchase #3 $219.83   7.366%   $236.0227   $236.02   $236.00   $236.00  
  Purchase #4 $197.30   13.470%   $223.8763   $223.88   $223.90   $223.90  
  Purchase #5 $232.71   9.649%   $255.1642   $255.16   $255.15   $255.20  
  Purchase #6 $33.42   12.259%   $37.517   $37.52   $37.50   $37.50  
  Purchase #7 $23.67   10.733%   $26.2105   $26.21   $26.20   $26.20  
  7 purchase totals = $788.20       $867.2663   $867.26   $867.20   $867.30