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 $162.99   7.307%   $174.8997   $174.90   $174.90   $174.90  
  Purchase #2 $89.25   7.687%   $96.1106   $96.11   $96.10   $96.10  
  Purchase #3 $135.27   13.469%   $153.4895   $153.49   $153.50   $153.50  
  Purchase #4 $139.66   11.861%   $156.2251   $156.23   $156.25   $156.20  
  Purchase #5 $69.82   8.637%   $75.8504   $75.85   $75.85   $75.90  
  Purchase #6 $135.72   11.714%   $151.6182   $151.62   $151.60   $151.60  
  Purchase #7 $189.88   12.862%   $214.3024   $214.30   $214.30   $214.30  
  7 purchase totals = $922.59       $1,022.4959   $1,022.50   $1,022.50   $1,022.50