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 $24.74   3.522%   $25.6113   $25.61   $25.60   $25.60  
  Purchase #2 $187.75   12.395%   $211.0216   $211.02   $211.00   $211.00  
  Purchase #3 $124.29   7.506%   $133.6192   $133.62   $133.60   $133.60  
  Purchase #4 $238.79   10.109%   $262.9293   $262.93   $262.95   $262.90  
  Purchase #5 $145.45   5.260%   $153.1007   $153.10   $153.10   $153.10  
  Purchase #6 $133.51   4.398%   $139.3818   $139.38   $139.40   $139.40  
  Purchase #7 $110.95   12.378%   $124.6834   $124.68   $124.70   $124.70  
  7 purchase totals = $965.48       $1,050.3473   $1,050.34   $1,050.35   $1,050.30