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 $175.62   5.138%   $184.6434   $184.64   $184.65   $184.60  
  Purchase #2 $215.98   9.238%   $235.9322   $235.93   $235.95   $235.90  
  Purchase #3 $218.59   6.824%   $233.5066   $233.51   $233.50   $233.50  
  Purchase #4 $238.32   12.117%   $267.1972   $267.20   $267.20   $267.20  
  Purchase #5 $207.46   11.753%   $231.8428   $231.84   $231.85   $231.80  
  Purchase #6 $200.41   5.517%   $211.4666   $211.47   $211.45   $211.50  
  Purchase #7 $239.67   4.223%   $249.7913   $249.79   $249.80   $249.80  
  7 purchase totals = $1,496.05       $1,614.3801   $1,614.38   $1,614.40   $1,614.30