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 $168.96   8.293%   $182.9719   $182.97   $182.95   $183.00  
  Purchase #2 $249.79   5.799%   $264.2753   $264.28   $264.30   $264.30  
  Purchase #3 $237.97   12.557%   $267.8519   $267.85   $267.85   $267.90  
  Purchase #4 $175.64   4.874%   $184.2007   $184.20   $184.20   $184.20  
  Purchase #5 $125.52   6.432%   $133.5934   $133.59   $133.60   $133.60  
  Purchase #6 $246.87   10.400%   $272.5445   $272.54   $272.55   $272.50  
  Purchase #7 $203.37   3.242%   $209.9633   $209.96   $209.95   $210.00  
  7 purchase totals = $1,408.12       $1,515.4010   $1,515.39   $1,515.40   $1,515.50