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 $152.67   4.352%   $159.3142   $159.31   $159.30   $159.30  
  Purchase #2 $39.67   8.648%   $43.1007   $43.10   $43.10   $43.10  
  Purchase #3 $230.36   6.657%   $245.6951   $245.70   $245.70   $245.70  
  Purchase #4 $224.30   5.488%   $236.6096   $236.61   $236.60   $236.60  
  Purchase #5 $73.94   3.653%   $76.641   $76.64   $76.65   $76.60  
  Purchase #6 $12.26   13.527%   $13.9184   $13.92   $13.90   $13.90  
  Purchase #7 $240.50   4.308%   $250.8607   $250.86   $250.85   $250.90  
  7 purchase totals = $973.70       $1,026.1397   $1,026.14   $1,026.10   $1,026.10