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 $56.99   4.664%   $59.648   $59.65   $59.65   $59.60  
  Purchase #2 $185.62   10.808%   $205.6818   $205.68   $205.70   $205.70  
  Purchase #3 $106.47   4.323%   $111.0727   $111.07   $111.05   $111.10  
  Purchase #4 $172.69   6.138%   $183.2897   $183.29   $183.30   $183.30  
  Purchase #5 $92.71   12.713%   $104.4962   $104.50   $104.50   $104.50  
  Purchase #6 $147.45   9.433%   $161.359   $161.36   $161.35   $161.40  
  Purchase #7 $74.36   7.588%   $80.0024   $80.00   $80.00   $80.00  
  7 purchase totals = $836.29       $905.5498   $905.55   $905.55   $905.60