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 $74.58   12.397%   $83.8257   $83.83   $83.85   $83.80  
  Purchase #2 $141.96   8.852%   $154.5263   $154.53   $154.55   $154.50  
  Purchase #3 $153.36   11.196%   $170.5302   $170.53   $170.55   $170.50  
  Purchase #4 $142.32   13.204%   $161.1119   $161.11   $161.10   $161.10  
  Purchase #5 $212.93   5.398%   $224.424   $224.42   $224.40   $224.40  
  Purchase #6 $247.73   7.722%   $266.8597   $266.86   $266.85   $266.90  
  Purchase #7 $166.73   4.219%   $173.7643   $173.76   $173.75   $173.80  
  7 purchase totals = $1,139.61       $1,235.0421   $1,235.04   $1,235.05   $1,235.00