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 $235.71   6.317%   $250.5998   $250.60   $250.60   $250.60  
  Purchase #2 $73.92   9.267%   $80.7702   $80.77   $80.75   $80.80  
  Purchase #3 $131.67   11.533%   $146.8555   $146.86   $146.85   $146.90  
  Purchase #4 $239.64   11.409%   $266.9805   $266.98   $267.00   $267.00  
  Purchase #5 $165.33   4.588%   $172.9153   $172.92   $172.90   $172.90  
  Purchase #6 $188.99   3.312%   $195.2493   $195.25   $195.25   $195.20  
  Purchase #7 $147.33   4.495%   $153.9525   $153.95   $153.95   $154.00  
  7 purchase totals = $1,182.59       $1,267.3231   $1,267.33   $1,267.30   $1,267.40