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 $48.68   9.402%   $53.2569   $53.26   $53.25   $53.30  
  Purchase #2 $83.81   13.680%   $95.2752   $95.28   $95.30   $95.30  
  Purchase #3 $29.35   9.194%   $32.0484   $32.05   $32.05   $32.00  
  Purchase #4 $249.56   6.356%   $265.422   $265.42   $265.40   $265.40  
  Purchase #5 $26.31   5.630%   $27.7913   $27.79   $27.80   $27.80  
  Purchase #6 $236.41   3.644%   $245.0248   $245.02   $245.00   $245.00  
  Purchase #7 $31.41   3.414%   $32.4823   $32.48   $32.50   $32.50  
  7 purchase totals = $705.53       $751.3009   $751.30   $751.30   $751.30