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 $68.77   4.148%   $71.6226   $71.62   $71.60   $71.60  
  Purchase #2 $22.26   11.707%   $24.866   $24.87   $24.85   $24.90  
  Purchase #3 $218.58   9.314%   $238.9385   $238.94   $238.95   $238.90  
  Purchase #4 $77.68   9.131%   $84.773   $84.77   $84.75   $84.80  
  Purchase #5 $78.72   5.426%   $82.9913   $82.99   $83.00   $83.00  
  Purchase #6 $42.46   4.359%   $44.3108   $44.31   $44.30   $44.30  
  Purchase #7 $214.47   9.317%   $234.4522   $234.45   $234.45   $234.50  
  7 purchase totals = $722.94       $781.9544   $781.95   $781.90   $782.00