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 $145.42   6.205%   $154.4433   $154.44   $154.45   $154.40  
  Purchase #2 $119.28   6.461%   $126.9867   $126.99   $127.00   $127.00  
  Purchase #3 $218.80   11.601%   $244.183   $244.18   $244.20   $244.20  
  Purchase #4 $187.53   13.765%   $213.3435   $213.34   $213.35   $213.30  
  Purchase #5 $204.30   5.202%   $214.9277   $214.93   $214.95   $214.90  
  Purchase #6 $55.34   7.222%   $59.3367   $59.34   $59.35   $59.30  
  Purchase #7 $59.86   5.173%   $62.9566   $62.96   $62.95   $63.00  
  7 purchase totals = $990.53       $1,076.1775   $1,076.18   $1,076.25   $1,076.10