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 $233.33   4.139%   $242.9875   $242.99   $243.00   $243.00  
  Purchase #2 $45.84   13.817%   $52.1737   $52.17   $52.15   $52.20  
  Purchase #3 $23.46   12.589%   $26.4134   $26.41   $26.40   $26.40  
  Purchase #4 $172.75   5.621%   $182.4603   $182.46   $182.45   $182.50  
  Purchase #5 $51.91   3.824%   $53.895   $53.90   $53.90   $53.90  
  Purchase #6 $238.74   11.384%   $265.9182   $265.92   $265.90   $265.90  
  Purchase #7 $214.27   10.294%   $236.327   $236.33   $236.35   $236.30  
  7 purchase totals = $980.30       $1,060.1751   $1,060.18   $1,060.15   $1,060.20