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 $231.36   12.382%   $260.007   $260.01   $260.00   $260.00  
  Purchase #2 $52.83   9.748%   $57.9799   $57.98   $58.00   $58.00  
  Purchase #3 $38.73   4.699%   $40.5499   $40.55   $40.55   $40.50  
  Purchase #4 $114.45   9.609%   $125.4475   $125.45   $125.45   $125.40  
  Purchase #5 $249.37   13.237%   $282.3791   $282.38   $282.40   $282.40  
  Purchase #6 $152.98   12.667%   $172.358   $172.36   $172.35   $172.40  
  Purchase #7 $110.58   4.740%   $115.8215   $115.82   $115.80   $115.80  
  7 purchase totals = $950.30       $1,054.5429   $1,054.55   $1,054.55   $1,054.50