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 $224.79   8.371%   $243.6072   $243.61   $243.60   $243.60  
  Purchase #2 $131.62   10.183%   $145.0229   $145.02   $145.00   $145.00  
  Purchase #3 $120.54   7.541%   $129.6299   $129.63   $129.65   $129.60  
  Purchase #4 $236.57   12.781%   $266.806   $266.81   $266.80   $266.80  
  Purchase #5 $27.84   12.242%   $31.2482   $31.25   $31.25   $31.20  
  Purchase #6 $150.78   8.239%   $163.2028   $163.20   $163.20   $163.20  
  Purchase #7 $15.85   6.648%   $16.9037   $16.90   $16.90   $16.90  
  7 purchase totals = $907.99       $996.4207   $996.42   $996.40   $996.30