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 $54.43   3.431%   $56.2975   $56.30   $56.30   $56.30  
  Purchase #2 $151.89   3.531%   $157.2532   $157.25   $157.25   $157.30  
  Purchase #3 $119.35   13.120%   $135.0087   $135.01   $135.00   $135.00  
  Purchase #4 $218.81   3.494%   $226.4552   $226.46   $226.45   $226.50  
  Purchase #5 $249.58   3.402%   $258.0707   $258.07   $258.05   $258.10  
  Purchase #6 $27.31   4.293%   $28.4824   $28.48   $28.50   $28.50  
  Purchase #7 $171.47   3.853%   $178.0767   $178.08   $178.10   $178.10  
  7 purchase totals = $992.84       $1,039.6444   $1,039.65   $1,039.65   $1,039.80