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 $119.54   12.660%   $134.6738   $134.67   $134.65   $134.70  
  Purchase #2 $212.68   4.309%   $221.8444   $221.84   $221.85   $221.80  
  Purchase #3 $68.63   8.320%   $74.34   $74.34   $74.35   $74.30  
  Purchase #4 $68.27   7.396%   $73.3192   $73.32   $73.30   $73.30  
  Purchase #5 $19.29   6.408%   $20.5261   $20.53   $20.55   $20.50  
  Purchase #6 $135.33   8.762%   $147.1876   $147.19   $147.20   $147.20  
  Purchase #7 $97.62   4.159%   $101.68   $101.68   $101.70   $101.70  
  7 purchase totals = $721.36       $773.5711   $773.57   $773.60   $773.50