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 $241.93   12.747%   $272.7688   $272.77   $272.75   $272.80  
  Purchase #2 $130.47   3.694%   $135.2896   $135.29   $135.30   $135.30  
  Purchase #3 $38.50   4.199%   $40.1166   $40.12   $40.10   $40.10  
  Purchase #4 $212.28   11.327%   $236.325   $236.33   $236.35   $236.30  
  Purchase #5 $49.43   3.770%   $51.2935   $51.29   $51.30   $51.30  
  Purchase #6 $66.79   4.187%   $69.5865   $69.59   $69.60   $69.60  
  Purchase #7 $183.78   9.482%   $201.206   $201.21   $201.20   $201.20  
  7 purchase totals = $923.18       $1,006.5860   $1,006.60   $1,006.60   $1,006.60