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 $202.85   11.852%   $226.8918   $226.89   $226.90   $226.90  
  Purchase #2 $124.57   6.653%   $132.8576   $132.86   $132.85   $132.90  
  Purchase #3 $35.35   4.587%   $36.9715   $36.97   $36.95   $37.00  
  Purchase #4 $110.36   6.127%   $117.1218   $117.12   $117.10   $117.10  
  Purchase #5 $158.25   6.788%   $168.992   $168.99   $169.00   $169.00  
  Purchase #6 $84.98   11.615%   $94.8504   $94.85   $94.85   $94.90  
  Purchase #7 $236.85   10.681%   $262.1479   $262.15   $262.15   $262.10  
  7 purchase totals = $953.21       $1,039.8330   $1,039.83   $1,039.80   $1,039.90