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 $75.62   12.649%   $85.1852   $85.19   $85.20   $85.20  
  Purchase #2 $119.26   6.472%   $126.9785   $126.98   $127.00   $127.00  
  Purchase #3 $44.87   3.211%   $46.3108   $46.31   $46.30   $46.30  
  Purchase #4 $65.29   13.128%   $73.8613   $73.86   $73.85   $73.90  
  Purchase #5 $134.60   5.762%   $142.3557   $142.36   $142.35   $142.40  
  Purchase #6 $72.81   3.727%   $75.5236   $75.52   $75.50   $75.50  
  Purchase #7 $121.56   6.178%   $129.07   $129.07   $129.05   $129.10  
  7 purchase totals = $634.01       $679.2851   $679.29   $679.25   $679.40