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 $248.74   5.454%   $262.3063   $262.31   $262.30   $262.30  
  Purchase #2 $234.48   4.251%   $244.4477   $244.45   $244.45   $244.40  
  Purchase #3 $117.46   4.855%   $123.1627   $123.16   $123.15   $123.20  
  Purchase #4 $76.57   8.690%   $83.2239   $83.22   $83.20   $83.20  
  Purchase #5 $204.78   4.866%   $214.7446   $214.74   $214.75   $214.70  
  Purchase #6 $158.78   4.873%   $166.5173   $166.52   $166.50   $166.50  
  Purchase #7 $134.52   13.759%   $153.0286   $153.03   $153.05   $153.00  
  7 purchase totals = $1,175.33       $1,247.4311   $1,247.43   $1,247.40   $1,247.30