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 $64.44   6.407%   $68.5687   $68.57   $68.55   $68.60  
  Purchase #2 $101.37   5.224%   $106.6656   $106.67   $106.65   $106.70  
  Purchase #3 $213.97   4.751%   $224.1357   $224.14   $224.15   $224.10  
  Purchase #4 $203.75   12.817%   $229.8646   $229.86   $229.85   $229.90  
  Purchase #5 $67.38   8.355%   $73.0096   $73.01   $73.00   $73.00  
  Purchase #6 $135.73   13.454%   $153.9911   $153.99   $154.00   $154.00  
  Purchase #7 $102.54   8.395%   $111.1482   $111.15   $111.15   $111.10  
  7 purchase totals = $889.18       $967.3835   $967.39   $967.35   $967.40