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 $246.36   4.837%   $258.2764   $258.28   $258.30   $258.30  
  Purchase #2 $204.93   10.340%   $226.1198   $226.12   $226.10   $226.10  
  Purchase #3 $160.47   8.602%   $174.2736   $174.27   $174.25   $174.30  
  Purchase #4 $198.80   11.467%   $221.5964   $221.60   $221.60   $221.60  
  Purchase #5 $214.59   9.361%   $234.6778   $234.68   $234.70   $234.70  
  Purchase #6 $139.66   5.290%   $147.048   $147.05   $147.05   $147.00  
  Purchase #7 $12.83   3.385%   $13.2643   $13.26   $13.25   $13.30  
  7 purchase totals = $1,177.64       $1,275.2563   $1,275.26   $1,275.25   $1,275.30