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 $61.35   5.172%   $64.523   $64.52   $64.50   $64.50  
  Purchase #2 $178.57   6.257%   $189.7431   $189.74   $189.75   $189.70  
  Purchase #3 $164.79   5.388%   $173.6689   $173.67   $173.65   $173.70  
  Purchase #4 $89.82   5.662%   $94.9056   $94.91   $94.90   $94.90  
  Purchase #5 $20.57   10.121%   $22.6519   $22.65   $22.65   $22.70  
  Purchase #6 $115.45   9.811%   $126.7768   $126.78   $126.80   $126.80  
  Purchase #7 $172.59   4.462%   $180.291   $180.29   $180.30   $180.30  
  7 purchase totals = $803.14       $852.5603   $852.56   $852.55   $852.60