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 $228.54   8.300%   $247.5088   $247.51   $247.50   $247.50  
  Purchase #2 $164.79   9.597%   $180.6049   $180.60   $180.60   $180.60  
  Purchase #3 $208.92   11.569%   $233.09   $233.09   $233.10   $233.10  
  Purchase #4 $100.66   11.551%   $112.2872   $112.29   $112.30   $112.30  
  Purchase #5 $152.78   8.551%   $165.8442   $165.84   $165.85   $165.80  
  Purchase #6 $24.68   7.643%   $26.5663   $26.57   $26.55   $26.60  
  Purchase #7 $71.66   13.277%   $81.1743   $81.17   $81.15   $81.20  
  7 purchase totals = $952.03       $1,047.0757   $1,047.07   $1,047.05   $1,047.10