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 $67.97   8.619%   $73.8283   $73.83   $73.85   $73.80  
  Purchase #2 $192.82   6.117%   $204.6148   $204.61   $204.60   $204.60  
  Purchase #3 $65.85   11.107%   $73.164   $73.16   $73.15   $73.20  
  Purchase #4 $180.29   13.274%   $204.2217   $204.22   $204.20   $204.20  
  Purchase #5 $68.47   4.211%   $71.3533   $71.35   $71.35   $71.40  
  Purchase #6 $136.57   5.111%   $143.5501   $143.55   $143.55   $143.60  
  Purchase #7 $150.34   13.186%   $170.1638   $170.16   $170.15   $170.20  
  7 purchase totals = $862.31       $940.8960   $940.88   $940.85   $941.00