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 $110.94   13.854%   $126.3096   $126.31   $126.30   $126.30  
  Purchase #2 $140.45   6.484%   $149.5568   $149.56   $149.55   $149.60  
  Purchase #3 $54.88   6.591%   $58.4971   $58.50   $58.50   $58.50  
  Purchase #4 $18.31   4.242%   $19.0867   $19.09   $19.10   $19.10  
  Purchase #5 $231.86   6.660%   $247.3019   $247.30   $247.30   $247.30  
  Purchase #6 $218.62   3.361%   $225.9678   $225.97   $225.95   $226.00  
  Purchase #7 $214.34   9.363%   $234.4087   $234.41   $234.40   $234.40  
  7 purchase totals = $989.40       $1,061.1286   $1,061.14   $1,061.10   $1,061.20