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 $125.99   12.708%   $142.0008   $142.00   $142.00   $142.00  
  Purchase #2 $204.93   6.871%   $219.0107   $219.01   $219.00   $219.00  
  Purchase #3 $30.64   7.321%   $32.8832   $32.88   $32.90   $32.90  
  Purchase #4 $155.97   12.694%   $175.7688   $175.77   $175.75   $175.80  
  Purchase #5 $198.37   11.295%   $220.7759   $220.78   $220.80   $220.80  
  Purchase #6 $14.26   13.429%   $16.175   $16.18   $16.20   $16.20  
  Purchase #7 $220.97   10.747%   $244.7176   $244.72   $244.70   $244.70  
  7 purchase totals = $951.13       $1,051.3320   $1,051.34   $1,051.35   $1,051.40