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 $152.72   6.165%   $162.1352   $162.14   $162.15   $162.10  
  Purchase #2 $169.99   9.805%   $186.6575   $186.66   $186.65   $186.70  
  Purchase #3 $150.88   9.512%   $165.2317   $165.23   $165.25   $165.20  
  Purchase #4 $65.52   6.486%   $69.7696   $69.77   $69.75   $69.80  
  Purchase #5 $204.86   11.575%   $228.5725   $228.57   $228.55   $228.60  
  Purchase #6 $80.28   9.792%   $88.141   $88.14   $88.15   $88.10  
  Purchase #7 $93.98   8.477%   $101.9467   $101.95   $101.95   $101.90  
  7 purchase totals = $918.23       $1,002.4542   $1,002.46   $1,002.45   $1,002.40