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 $241.47   13.749%   $274.6697   $274.67   $274.65   $274.70  
  Purchase #2 $172.39   10.861%   $191.1133   $191.11   $191.10   $191.10  
  Purchase #3 $228.55   3.159%   $235.7699   $235.77   $235.75   $235.80  
  Purchase #4 $168.45   7.161%   $180.5127   $180.51   $180.50   $180.50  
  Purchase #5 $32.41   3.788%   $33.6377   $33.64   $33.65   $33.60  
  Purchase #6 $156.84   9.461%   $171.6786   $171.68   $171.70   $171.70  
  Purchase #7 $67.29   7.652%   $72.439   $72.44   $72.45   $72.40  
  7 purchase totals = $1,067.40       $1,159.8209   $1,159.82   $1,159.80   $1,159.80