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 $44.71   9.569%   $48.9883   $48.99   $49.00   $49.00  
  Purchase #2 $5.85   6.806%   $6.2482   $6.25   $6.25   $6.20  
  Purchase #3 $68.30   13.781%   $77.7124   $77.71   $77.70   $77.70  
  Purchase #4 $238.90   12.444%   $268.6287   $268.63   $268.65   $268.60  
  Purchase #5 $235.88   6.415%   $251.0117   $251.01   $251.00   $251.00  
  Purchase #6 $175.48   6.117%   $186.2141   $186.21   $186.20   $186.20  
  Purchase #7 $224.99   4.139%   $234.3023   $234.30   $234.30   $234.30  
  7 purchase totals = $994.11       $1,073.1057   $1,073.10   $1,073.10   $1,073.00