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 $241.98   12.471%   $272.1573   $272.16   $272.15   $272.20  
  Purchase #2 $92.78   10.595%   $102.61   $102.61   $102.60   $102.60  
  Purchase #3 $89.92   13.362%   $101.9351   $101.94   $101.95   $101.90  
  Purchase #4 $158.38   10.422%   $174.8864   $174.89   $174.90   $174.90  
  Purchase #5 $212.30   3.235%   $219.1679   $219.17   $219.15   $219.20  
  Purchase #6 $238.62   5.858%   $252.5984   $252.60   $252.60   $252.60  
  Purchase #7 $118.91   6.337%   $126.4453   $126.45   $126.45   $126.40  
  7 purchase totals = $1,152.89       $1,249.8004   $1,249.82   $1,249.80   $1,249.80