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 $244.73   3.649%   $253.6602   $253.66   $253.65   $253.70  
  Purchase #2 $54.31   8.527%   $58.941   $58.94   $58.95   $58.90  
  Purchase #3 $67.88   4.711%   $71.0778   $71.08   $71.10   $71.10  
  Purchase #4 $58.58   12.118%   $65.6787   $65.68   $65.70   $65.70  
  Purchase #5 $40.88   11.366%   $45.5264   $45.53   $45.55   $45.50  
  Purchase #6 $150.37   10.666%   $166.4085   $166.41   $166.40   $166.40  
  Purchase #7 $193.87   12.735%   $218.5593   $218.56   $218.55   $218.60  
  7 purchase totals = $810.62       $879.8519   $879.86   $879.90   $879.90