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 $119.91   4.605%   $125.4319   $125.43   $125.45   $125.40  
  Purchase #2 $136.48   11.838%   $152.6365   $152.64   $152.65   $152.60  
  Purchase #3 $43.90   12.344%   $49.319   $49.32   $49.30   $49.30  
  Purchase #4 $23.67   3.442%   $24.4847   $24.48   $24.50   $24.50  
  Purchase #5 $181.90   7.723%   $195.9481   $195.95   $195.95   $195.90  
  Purchase #6 $194.72   12.231%   $218.5362   $218.54   $218.55   $218.50  
  Purchase #7 $56.52   11.549%   $63.0475   $63.05   $63.05   $63.00  
  7 purchase totals = $757.10       $829.4039   $829.41   $829.45   $829.20