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 $160.61   10.132%   $176.883   $176.88   $176.90   $176.90  
  Purchase #2 $148.82   3.589%   $154.1611   $154.16   $154.15   $154.20  
  Purchase #3 $55.40   13.836%   $63.0651   $63.07   $63.05   $63.10  
  Purchase #4 $44.41   11.106%   $49.3422   $49.34   $49.35   $49.30  
  Purchase #5 $73.69   10.106%   $81.1371   $81.14   $81.15   $81.10  
  Purchase #6 $145.73   8.635%   $158.3138   $158.31   $158.30   $158.30  
  Purchase #7 $223.87   13.483%   $254.0544   $254.05   $254.05   $254.10  
  7 purchase totals = $852.53       $936.9567   $936.95   $936.95   $937.00