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 $94.63   13.433%   $107.3416   $107.34   $107.35   $107.30  
  Purchase #2 $240.73   10.106%   $265.0582   $265.06   $265.05   $265.10  
  Purchase #3 $203.41   13.608%   $231.09   $231.09   $231.10   $231.10  
  Purchase #4 $218.26   7.293%   $234.1777   $234.18   $234.20   $234.20  
  Purchase #5 $88.71   6.782%   $94.7263   $94.73   $94.75   $94.70  
  Purchase #6 $24.51   12.826%   $27.6537   $27.65   $27.65   $27.70  
  Purchase #7 $94.78   7.527%   $101.9141   $101.91   $101.90   $101.90  
  7 purchase totals = $965.03       $1,061.9616   $1,061.96   $1,062.00   $1,062.00