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 $230.61   3.642%   $239.0088   $239.01   $239.00   $239.00  
  Purchase #2 $185.96   11.651%   $207.6262   $207.63   $207.65   $207.60  
  Purchase #3 $95.86   11.280%   $106.673   $106.67   $106.65   $106.70  
  Purchase #4 $92.70   8.112%   $100.2198   $100.22   $100.20   $100.20  
  Purchase #5 $23.29   4.185%   $24.2647   $24.26   $24.25   $24.30  
  Purchase #6 $212.91   5.690%   $225.0246   $225.02   $225.00   $225.00  
  Purchase #7 $41.43   6.785%   $44.241   $44.24   $44.25   $44.20  
  7 purchase totals = $882.76       $947.0581   $947.05   $947.00   $947.00