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 $231.27   11.632%   $258.1713   $258.17   $258.15   $258.20  
  Purchase #2 $180.89   4.313%   $188.6918   $188.69   $188.70   $188.70  
  Purchase #3 $49.50   9.569%   $54.2367   $54.24   $54.25   $54.20  
  Purchase #4 $26.56   6.845%   $28.378   $28.38   $28.40   $28.40  
  Purchase #5 $93.33   13.348%   $105.7877   $105.79   $105.80   $105.80  
  Purchase #6 $219.53   10.461%   $242.495   $242.50   $242.50   $242.50  
  Purchase #7 $158.52   7.707%   $170.7371   $170.74   $170.75   $170.70  
  7 purchase totals = $959.60       $1,048.4976   $1,048.51   $1,048.55   $1,048.50