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 $54.68   13.368%   $61.9896   $61.99   $62.00   $62.00  
  Purchase #2 $14.91   5.784%   $15.7724   $15.77   $15.75   $15.80  
  Purchase #3 $111.39   6.388%   $118.5056   $118.51   $118.50   $118.50  
  Purchase #4 $9.92   10.393%   $10.951   $10.95   $10.95   $11.00  
  Purchase #5 $233.50   4.437%   $243.8604   $243.86   $243.85   $243.90  
  Purchase #6 $140.39   7.507%   $150.9291   $150.93   $150.95   $150.90  
  Purchase #7 $9.95   9.799%   $10.925   $10.93   $10.95   $10.90  
  7 purchase totals = $574.74       $612.9331   $612.94   $612.95   $613.00