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 $85.57   7.693%   $92.1529   $92.15   $92.15   $92.20  
  Purchase #2 $36.98   10.773%   $40.9639   $40.96   $40.95   $41.00  
  Purchase #3 $60.59   4.192%   $63.1299   $63.13   $63.15   $63.10  
  Purchase #4 $111.43   9.288%   $121.7796   $121.78   $121.80   $121.80  
  Purchase #5 $29.25   6.675%   $31.2024   $31.20   $31.20   $31.20  
  Purchase #6 $183.58   4.856%   $192.4946   $192.49   $192.50   $192.50  
  Purchase #7 $194.86   13.546%   $221.2557   $221.26   $221.25   $221.30  
  7 purchase totals = $702.26       $762.9790   $762.97   $763.00   $763.10