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 $69.76   10.863%   $77.338   $77.34   $77.35   $77.30  
  Purchase #2 $235.55   10.234%   $259.6562   $259.66   $259.65   $259.70  
  Purchase #3 $158.48   3.301%   $163.7114   $163.71   $163.70   $163.70  
  Purchase #4 $234.67   12.788%   $264.6796   $264.68   $264.70   $264.70  
  Purchase #5 $46.96   10.817%   $52.0397   $52.04   $52.05   $52.00  
  Purchase #6 $209.40   4.856%   $219.5685   $219.57   $219.55   $219.60  
  Purchase #7 $68.38   12.459%   $76.8995   $76.90   $76.90   $76.90  
  7 purchase totals = $1,023.20       $1,113.8929   $1,113.90   $1,113.90   $1,113.90