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 $160.89   8.608%   $174.7394   $174.74   $174.75   $174.70  
  Purchase #2 $119.25   11.184%   $132.5869   $132.59   $132.60   $132.60  
  Purchase #3 $213.98   13.386%   $242.6234   $242.62   $242.60   $242.60  
  Purchase #4 $152.26   10.639%   $168.4589   $168.46   $168.45   $168.50  
  Purchase #5 $180.67   6.287%   $192.0287   $192.03   $192.05   $192.00  
  Purchase #6 $113.65   4.723%   $119.0177   $119.02   $119.00   $119.00  
  Purchase #7 $13.46   6.719%   $14.3644   $14.36   $14.35   $14.40  
  7 purchase totals = $954.16       $1,043.8194   $1,043.82   $1,043.80   $1,043.80