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 $178.60   8.775%   $194.2722   $194.27   $194.25   $194.30  
  Purchase #2 $247.26   8.323%   $267.8394   $267.84   $267.85   $267.80  
  Purchase #3 $65.99   9.497%   $72.2571   $72.26   $72.25   $72.30  
  Purchase #4 $132.68   6.546%   $141.3652   $141.37   $141.35   $141.40  
  Purchase #5 $86.25   4.665%   $90.2736   $90.27   $90.25   $90.30  
  Purchase #6 $119.62   4.524%   $125.0316   $125.03   $125.05   $125.00  
  Purchase #7 $16.82   10.753%   $18.6287   $18.63   $18.65   $18.60  
  7 purchase totals = $847.22       $909.6678   $909.67   $909.65   $909.70