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 $203.54   11.779%   $227.515   $227.52   $227.50   $227.50  
  Purchase #2 $67.46   13.328%   $76.4511   $76.45   $76.45   $76.50  
  Purchase #3 $102.35   3.479%   $105.9108   $105.91   $105.90   $105.90  
  Purchase #4 $168.43   12.458%   $189.413   $189.41   $189.40   $189.40  
  Purchase #5 $122.92   6.211%   $130.5546   $130.55   $130.55   $130.60  
  Purchase #6 $17.48   4.613%   $18.2864   $18.29   $18.30   $18.30  
  Purchase #7 $194.84   7.613%   $209.6732   $209.67   $209.65   $209.70  
  7 purchase totals = $877.02       $957.8041   $957.80   $957.75   $957.90