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 $110.83   10.106%   $122.0305   $122.03   $122.05   $122.00  
  Purchase #2 $196.99   11.201%   $219.0548   $219.05   $219.05   $219.10  
  Purchase #3 $158.72   9.669%   $174.0666   $174.07   $174.05   $174.10  
  Purchase #4 $44.57   13.365%   $50.5268   $50.53   $50.55   $50.50  
  Purchase #5 $60.64   6.245%   $64.427   $64.43   $64.45   $64.40  
  Purchase #6 $149.87   4.370%   $156.4193   $156.42   $156.40   $156.40  
  Purchase #7 $239.99   12.161%   $269.1752   $269.18   $269.20   $269.20  
  7 purchase totals = $961.61       $1,055.7002   $1,055.71   $1,055.75   $1,055.70