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 $45.52   5.468%   $48.009   $48.01   $48.00   $48.00  
  Purchase #2 $229.66   4.510%   $240.0177   $240.02   $240.00   $240.00  
  Purchase #3 $163.97   6.156%   $174.064   $174.06   $174.05   $174.10  
  Purchase #4 $23.96   9.168%   $26.1567   $26.16   $26.15   $26.20  
  Purchase #5 $146.66   13.598%   $166.6028   $166.60   $166.60   $166.60  
  Purchase #6 $160.38   5.459%   $169.1351   $169.14   $169.15   $169.10  
  Purchase #7 $182.84   6.224%   $194.22   $194.22   $194.20   $194.20  
  7 purchase totals = $952.99       $1,018.2053   $1,018.21   $1,018.15   $1,018.20