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 $247.35   11.176%   $274.9938   $274.99   $275.00   $275.00  
  Purchase #2 $159.84   3.120%   $164.827   $164.83   $164.85   $164.80  
  Purchase #3 $130.39   11.427%   $145.2897   $145.29   $145.30   $145.30  
  Purchase #4 $165.77   11.290%   $184.4854   $184.49   $184.50   $184.50  
  Purchase #5 $54.45   6.563%   $58.0236   $58.02   $58.00   $58.00  
  Purchase #6 $113.32   13.408%   $128.5139   $128.51   $128.50   $128.50  
  Purchase #7 $150.30   5.231%   $158.1622   $158.16   $158.15   $158.20  
  7 purchase totals = $1,021.42       $1,114.2956   $1,114.29   $1,114.30   $1,114.30