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 $201.46   8.710%   $219.0072   $219.01   $219.00   $219.00  
  Purchase #2 $60.99   10.738%   $67.5391   $67.54   $67.55   $67.50  
  Purchase #3 $66.70   6.512%   $71.0435   $71.04   $71.05   $71.00  
  Purchase #4 $228.31   13.843%   $259.915   $259.92   $259.90   $259.90  
  Purchase #5 $26.41   13.582%   $29.997   $30.00   $30.00   $30.00  
  Purchase #6 $149.41   9.516%   $163.6279   $163.63   $163.65   $163.60  
  Purchase #7 $90.34   4.467%   $94.3755   $94.38   $94.40   $94.40  
  7 purchase totals = $823.62       $905.5052   $905.52   $905.55   $905.40