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 $247.35   7.146%   $265.0256   $265.03   $265.05   $265.00  
  Purchase #2 $145.42   9.547%   $159.3032   $159.30   $159.30   $159.30  
  Purchase #3 $242.95   11.489%   $270.8625   $270.86   $270.85   $270.90  
  Purchase #4 $83.67   13.503%   $94.968   $94.97   $94.95   $95.00  
  Purchase #5 $115.64   7.872%   $124.7432   $124.74   $124.75   $124.70  
  Purchase #6 $26.26   12.728%   $29.6024   $29.60   $29.60   $29.60  
  Purchase #7 $153.39   8.345%   $166.1904   $166.19   $166.20   $166.20  
  7 purchase totals = $1,014.68       $1,110.6953   $1,110.69   $1,110.70   $1,110.70