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 $248.43   5.601%   $262.3446   $262.34   $262.35   $262.30  
  Purchase #2 $131.39   6.729%   $140.2312   $140.23   $140.25   $140.20  
  Purchase #3 $78.81   6.595%   $84.0075   $84.01   $84.00   $84.00  
  Purchase #4 $110.95   11.547%   $123.7614   $123.76   $123.75   $123.80  
  Purchase #5 $39.99   13.260%   $45.2927   $45.29   $45.30   $45.30  
  Purchase #6 $86.27   12.179%   $96.7768   $96.78   $96.80   $96.80  
  Purchase #7 $96.82   12.439%   $108.8634   $108.86   $108.85   $108.90  
  7 purchase totals = $792.66       $861.2776   $861.27   $861.30   $861.30