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 $58.68   8.488%   $63.6608   $63.66   $63.65   $63.70  
  Purchase #2 $105.70   7.818%   $113.9636   $113.96   $113.95   $114.00  
  Purchase #3 $80.83   12.437%   $90.8828   $90.88   $90.90   $90.90  
  Purchase #4 $142.72   13.763%   $162.3626   $162.36   $162.35   $162.40  
  Purchase #5 $95.84   6.446%   $102.0178   $102.02   $102.00   $102.00  
  Purchase #6 $112.78   10.168%   $124.2475   $124.25   $124.25   $124.20  
  Purchase #7 $104.91   10.792%   $116.2319   $116.23   $116.25   $116.20  
  7 purchase totals = $701.46       $773.3670   $773.36   $773.35   $773.40