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 $68.64   10.103%   $75.5747   $75.57   $75.55   $75.60  
  Purchase #2 $186.48   10.823%   $206.6627   $206.66   $206.65   $206.70  
  Purchase #3 $5.43   9.266%   $5.9331   $5.93   $5.95   $5.90  
  Purchase #4 $54.37   4.568%   $56.8536   $56.85   $56.85   $56.90  
  Purchase #5 $54.46   8.655%   $59.1735   $59.17   $59.15   $59.20  
  Purchase #6 $168.35   8.481%   $182.6278   $182.63   $182.65   $182.60  
  Purchase #7 $150.67   12.694%   $169.796   $169.80   $169.80   $169.80  
  7 purchase totals = $688.40       $756.6214   $756.61   $756.60   $756.70