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 $129.82   8.747%   $141.1754   $141.18   $141.20   $141.20  
  Purchase #2 $152.93   3.362%   $158.0715   $158.07   $158.05   $158.10  
  Purchase #3 $184.43   5.161%   $193.9484   $193.95   $193.95   $193.90  
  Purchase #4 $246.64   6.440%   $262.5236   $262.52   $262.50   $262.50  
  Purchase #5 $87.34   5.181%   $91.8651   $91.87   $91.85   $91.90  
  Purchase #6 $214.58   9.747%   $235.4951   $235.50   $235.50   $235.50  
  Purchase #7 $75.48   10.237%   $83.2069   $83.21   $83.20   $83.20  
  7 purchase totals = $1,091.22       $1,166.2860   $1,166.30   $1,166.25   $1,166.30