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 $57.27   11.756%   $64.0027   $64.00   $64.00   $64.00  
  Purchase #2 $196.33   10.255%   $216.4636   $216.46   $216.45   $216.50  
  Purchase #3 $71.58   8.346%   $77.5541   $77.55   $77.55   $77.60  
  Purchase #4 $237.94   7.591%   $256.002   $256.00   $256.00   $256.00  
  Purchase #5 $119.89   13.114%   $135.6124   $135.61   $135.60   $135.60  
  Purchase #6 $18.70   3.306%   $19.3182   $19.32   $19.30   $19.30  
  Purchase #7 $240.30   10.517%   $265.5724   $265.57   $265.55   $265.60  
  7 purchase totals = $942.01       $1,034.5254   $1,034.51   $1,034.45   $1,034.60