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 $58.25   4.762%   $61.0239   $61.02   $61.00   $61.00  
  Purchase #2 $216.38   5.586%   $228.467   $228.47   $228.45   $228.50  
  Purchase #3 $246.63   13.349%   $279.5526   $279.55   $279.55   $279.60  
  Purchase #4 $13.61   12.152%   $15.2639   $15.26   $15.25   $15.30  
  Purchase #5 $129.70   5.569%   $136.923   $136.92   $136.90   $136.90  
  Purchase #6 $167.67   11.801%   $187.4567   $187.46   $187.45   $187.50  
  Purchase #7 $222.85   4.241%   $232.3011   $232.30   $232.30   $232.30  
  7 purchase totals = $1,055.09       $1,140.9882   $1,140.98   $1,140.90   $1,141.10