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 $56.88   6.355%   $60.4947   $60.49   $60.50   $60.50  
  Purchase #2 $245.36   3.832%   $254.7622   $254.76   $254.75   $254.80  
  Purchase #3 $141.62   9.506%   $155.0824   $155.08   $155.10   $155.10  
  Purchase #4 $178.73   11.764%   $199.7558   $199.76   $199.75   $199.80  
  Purchase #5 $129.40   11.432%   $144.193   $144.19   $144.20   $144.20  
  Purchase #6 $91.41   11.103%   $101.5593   $101.56   $101.55   $101.60  
  Purchase #7 $93.78   3.364%   $96.9348   $96.93   $96.95   $96.90  
  7 purchase totals = $937.18       $1,012.7822   $1,012.77   $1,012.80   $1,012.90