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 $54.59   11.190%   $60.6986   $60.70   $60.70   $60.70  
  Purchase #2 $250.79   8.528%   $272.1774   $272.18   $272.20   $272.20  
  Purchase #3 $250.90   10.695%   $277.7338   $277.73   $277.75   $277.70  
  Purchase #4 $125.65   3.764%   $130.3795   $130.38   $130.40   $130.40  
  Purchase #5 $126.86   6.860%   $135.5626   $135.56   $135.55   $135.60  
  Purchase #6 $134.31   3.824%   $139.446   $139.45   $139.45   $139.40  
  Purchase #7 $190.95   4.827%   $200.1672   $200.17   $200.15   $200.20  
  7 purchase totals = $1,134.05       $1,216.1651   $1,216.17   $1,216.20   $1,216.20