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 $59.83   10.856%   $66.3251   $66.33   $66.35   $66.30  
  Purchase #2 $174.48   13.801%   $198.56   $198.56   $198.55   $198.60  
  Purchase #3 $184.55   9.793%   $202.623   $202.62   $202.60   $202.60  
  Purchase #4 $144.49   11.420%   $160.9908   $160.99   $161.00   $161.00  
  Purchase #5 $113.60   8.450%   $123.1992   $123.20   $123.20   $123.20  
  Purchase #6 $87.90   11.430%   $97.947   $97.95   $97.95   $97.90  
  Purchase #7 $119.46   5.560%   $126.102   $126.10   $126.10   $126.10  
  7 purchase totals = $884.31       $975.7471   $975.75   $975.75   $975.70