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 $56.64   5.176%   $59.5717   $59.57   $59.55   $59.60  
  Purchase #2 $191.70   13.590%   $217.752   $217.75   $217.75   $217.80  
  Purchase #3 $205.90   4.552%   $215.2726   $215.27   $215.25   $215.30  
  Purchase #4 $189.93   5.393%   $200.1729   $200.17   $200.15   $200.20  
  Purchase #5 $55.48   5.523%   $58.5442   $58.54   $58.55   $58.50  
  Purchase #6 $93.76   4.220%   $97.7167   $97.72   $97.70   $97.70  
  Purchase #7 $161.55   11.612%   $180.3092   $180.31   $180.30   $180.30  
  7 purchase totals = $954.96       $1,029.3393   $1,029.33   $1,029.25   $1,029.40