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 $204.33   5.356%   $215.2739   $215.27   $215.25   $215.30  
  Purchase #2 $116.95   3.327%   $120.8409   $120.84   $120.85   $120.80  
  Purchase #3 $183.46   8.114%   $198.3459   $198.35   $198.35   $198.30  
  Purchase #4 $236.38   6.844%   $252.5578   $252.56   $252.55   $252.60  
  Purchase #5 $41.83   6.635%   $44.6054   $44.61   $44.60   $44.60  
  Purchase #6 $60.35   9.241%   $65.9269   $65.93   $65.95   $65.90  
  Purchase #7 $60.32   13.507%   $68.4674   $68.47   $68.45   $68.50  
  7 purchase totals = $903.62       $966.0182   $966.03   $966.00   $966.00