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 $79.77   5.240%   $83.9499   $83.95   $83.95   $83.90  
  Purchase #2 $61.77   10.654%   $68.351   $68.35   $68.35   $68.40  
  Purchase #3 $42.35   13.241%   $47.9576   $47.96   $47.95   $48.00  
  Purchase #4 $249.90   6.770%   $266.8182   $266.82   $266.80   $266.80  
  Purchase #5 $14.45   5.865%   $15.2975   $15.30   $15.30   $15.30  
  Purchase #6 $210.79   6.159%   $223.7726   $223.77   $223.75   $223.80  
  Purchase #7 $26.61   10.413%   $29.3809   $29.38   $29.40   $29.40  
  7 purchase totals = $685.64       $735.5277   $735.53   $735.50   $735.60