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 $246.84   10.377%   $272.4546   $272.45   $272.45   $272.50  
  Purchase #2 $63.34   9.114%   $69.1128   $69.11   $69.10   $69.10  
  Purchase #3 $128.55   4.259%   $134.0249   $134.02   $134.00   $134.00  
  Purchase #4 $188.63   3.515%   $195.2603   $195.26   $195.25   $195.30  
  Purchase #5 $241.79   7.846%   $260.7608   $260.76   $260.75   $260.80  
  Purchase #6 $31.77   7.544%   $34.1667   $34.17   $34.15   $34.20  
  Purchase #7 $219.38   8.543%   $238.1216   $238.12   $238.10   $238.10  
  7 purchase totals = $1,120.30       $1,203.9017   $1,203.89   $1,203.80   $1,204.00