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 $67.93   7.650%   $73.1266   $73.13   $73.15   $73.10  
  Purchase #2 $44.57   3.373%   $46.0733   $46.07   $46.05   $46.10  
  Purchase #3 $212.67   7.184%   $227.9482   $227.95   $227.95   $227.90  
  Purchase #4 $96.27   10.139%   $106.0308   $106.03   $106.05   $106.00  
  Purchase #5 $85.73   5.731%   $90.6432   $90.64   $90.65   $90.60  
  Purchase #6 $29.42   3.535%   $30.46   $30.46   $30.45   $30.50  
  Purchase #7 $161.34   12.388%   $181.3268   $181.33   $181.35   $181.30  
  7 purchase totals = $697.93       $755.6089   $755.61   $755.65   $755.50