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 $93.97   11.641%   $104.909   $104.91   $104.90   $104.90  
  Purchase #2 $107.33   13.256%   $121.5577   $121.56   $121.55   $121.60  
  Purchase #3 $88.84   3.728%   $92.152   $92.15   $92.15   $92.20  
  Purchase #4 $119.49   4.713%   $125.1216   $125.12   $125.10   $125.10  
  Purchase #5 $23.40   10.483%   $25.853   $25.85   $25.85   $25.90  
  Purchase #6 $200.97   12.596%   $226.2842   $226.28   $226.30   $226.30  
  Purchase #7 $192.89   12.650%   $217.2906   $217.29   $217.30   $217.30  
  7 purchase totals = $826.89       $913.1681   $913.16   $913.15   $913.30