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 $60.86   3.775%   $63.1575   $63.16   $63.15   $63.20  
  Purchase #2 $97.42   13.122%   $110.2035   $110.20   $110.20   $110.20  
  Purchase #3 $63.27   12.159%   $70.963   $70.96   $70.95   $71.00  
  Purchase #4 $233.65   8.239%   $252.9004   $252.90   $252.90   $252.90  
  Purchase #5 $163.56   8.303%   $177.1404   $177.14   $177.15   $177.10  
  Purchase #6 $108.89   11.773%   $121.7096   $121.71   $121.70   $121.70  
  Purchase #7 $83.66   10.310%   $92.2853   $92.29   $92.30   $92.30  
  7 purchase totals = $811.31       $888.3597   $888.36   $888.35   $888.40