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 $61.59   8.621%   $66.8997   $66.90   $66.90   $66.90  
  Purchase #2 $151.64   6.157%   $160.9765   $160.98   $161.00   $161.00  
  Purchase #3 $48.34   6.566%   $51.514   $51.51   $51.50   $51.50  
  Purchase #4 $187.98   6.789%   $200.742   $200.74   $200.75   $200.70  
  Purchase #5 $136.74   9.836%   $150.1897   $150.19   $150.20   $150.20  
  Purchase #6 $82.99   10.635%   $91.816   $91.82   $91.80   $91.80  
  Purchase #7 $70.99   5.521%   $74.9094   $74.91   $74.90   $74.90  
  7 purchase totals = $740.27       $797.0473   $797.05   $797.05   $797.00