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 $64.64   13.551%   $73.3994   $73.40   $73.40   $73.40  
  Purchase #2 $36.48   13.565%   $41.4285   $41.43   $41.45   $41.40  
  Purchase #3 $227.36   7.858%   $245.2259   $245.23   $245.25   $245.20  
  Purchase #4 $23.42   9.113%   $25.5543   $25.55   $25.55   $25.60  
  Purchase #5 $238.39   11.224%   $265.1469   $265.15   $265.15   $265.10  
  Purchase #6 $237.49   6.413%   $252.7202   $252.72   $252.70   $252.70  
  Purchase #7 $80.33   10.259%   $88.5711   $88.57   $88.55   $88.60  
  7 purchase totals = $908.11       $992.0463   $992.05   $992.05   $992.00