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 $37.96   8.776%   $41.2914   $41.29   $41.30   $41.30  
  Purchase #2 $217.92   11.437%   $242.8435   $242.84   $242.85   $242.80  
  Purchase #3 $151.97   7.761%   $163.7644   $163.76   $163.75   $163.80  
  Purchase #4 $219.69   7.329%   $235.7911   $235.79   $235.80   $235.80  
  Purchase #5 $112.42   11.864%   $125.7575   $125.76   $125.75   $125.80  
  Purchase #6 $179.73   13.830%   $204.5867   $204.59   $204.60   $204.60  
  Purchase #7 $64.63   5.395%   $68.1168   $68.12   $68.10   $68.10  
  7 purchase totals = $984.32       $1,082.1514   $1,082.15   $1,082.15   $1,082.20