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 $51.94   13.655%   $59.0324   $59.03   $59.05   $59.00  
  Purchase #2 $246.34   10.328%   $271.782   $271.78   $271.80   $271.80  
  Purchase #3 $62.28   10.554%   $68.853   $68.85   $68.85   $68.90  
  Purchase #4 $18.46   6.465%   $19.6534   $19.65   $19.65   $19.70  
  Purchase #5 $219.60   9.190%   $239.7812   $239.78   $239.80   $239.80  
  Purchase #6 $201.92   5.730%   $213.49   $213.49   $213.50   $213.50  
  Purchase #7 $124.66   4.721%   $130.5452   $130.55   $130.55   $130.50  
  7 purchase totals = $925.20       $1,003.1372   $1,003.13   $1,003.20   $1,003.20