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 $61.52   6.798%   $65.7021   $65.70   $65.70   $65.70  
  Purchase #2 $239.48   7.190%   $256.6986   $256.70   $256.70   $256.70  
  Purchase #3 $150.62   12.727%   $169.7894   $169.79   $169.80   $169.80  
  Purchase #4 $29.35   13.364%   $33.2723   $33.27   $33.25   $33.30  
  Purchase #5 $95.92   5.813%   $101.4958   $101.50   $101.50   $101.50  
  Purchase #6 $26.48   8.267%   $28.6691   $28.67   $28.65   $28.70  
  Purchase #7 $54.87   5.147%   $57.6942   $57.69   $57.70   $57.70  
  7 purchase totals = $658.24       $713.3215   $713.32   $713.30   $713.40