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 $164.81   13.455%   $186.9852   $186.99   $187.00   $187.00  
  Purchase #2 $226.43   11.427%   $252.3042   $252.30   $252.30   $252.30  
  Purchase #3 $145.50   6.121%   $154.4061   $154.41   $154.40   $154.40  
  Purchase #4 $157.70   3.618%   $163.4056   $163.41   $163.40   $163.40  
  Purchase #5 $47.32   7.217%   $50.7351   $50.74   $50.75   $50.70  
  Purchase #6 $137.51   11.375%   $153.1518   $153.15   $153.15   $153.20  
  Purchase #7 $87.47   5.175%   $91.9966   $92.00   $92.00   $92.00  
  7 purchase totals = $966.74       $1,052.9846   $1,053.00   $1,053.00   $1,053.00