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 $62.33   10.556%   $68.9096   $68.91   $68.90   $68.90  
  Purchase #2 $72.33   10.121%   $79.6505   $79.65   $79.65   $79.70  
  Purchase #3 $111.92   4.418%   $116.8646   $116.86   $116.85   $116.90  
  Purchase #4 $152.69   8.353%   $165.4442   $165.44   $165.45   $165.40  
  Purchase #5 $150.42   12.371%   $169.0285   $169.03   $169.05   $169.00  
  Purchase #6 $62.68   13.820%   $71.3424   $71.34   $71.35   $71.30  
  Purchase #7 $132.91   3.633%   $137.7386   $137.74   $137.75   $137.70  
  7 purchase totals = $745.28       $808.9784   $808.97   $809.00   $808.90