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 $95.67   10.207%   $105.435   $105.44   $105.45   $105.40  
  Purchase #2 $228.79   5.393%   $241.1286   $241.13   $241.15   $241.10  
  Purchase #3 $120.29   4.317%   $125.4829   $125.48   $125.50   $125.50  
  Purchase #4 $219.85   3.626%   $227.8218   $227.82   $227.80   $227.80  
  Purchase #5 $247.26   8.103%   $267.2955   $267.30   $267.30   $267.30  
  Purchase #6 $47.75   11.444%   $53.2145   $53.21   $53.20   $53.20  
  Purchase #7 $30.62   11.812%   $34.2368   $34.24   $34.25   $34.20  
  7 purchase totals = $990.23       $1,054.6151   $1,054.62   $1,054.65   $1,054.50