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 $51.43   13.807%   $58.5309   $58.53   $58.55   $58.50  
  Purchase #2 $250.73   7.109%   $268.5544   $268.55   $268.55   $268.60  
  Purchase #3 $32.28   13.718%   $36.7082   $36.71   $36.70   $36.70  
  Purchase #4 $143.48   7.651%   $154.4577   $154.46   $154.45   $154.50  
  Purchase #5 $94.98   13.650%   $107.9448   $107.94   $107.95   $107.90  
  Purchase #6 $67.95   11.793%   $75.9633   $75.96   $75.95   $76.00  
  Purchase #7 $248.67   3.787%   $258.0871   $258.09   $258.10   $258.10  
  7 purchase totals = $889.52       $960.2464   $960.24   $960.25   $960.30