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 $88.71   3.677%   $91.9719   $91.97   $91.95   $92.00  
  Purchase #2 $154.44   5.274%   $162.5852   $162.59   $162.60   $162.60  
  Purchase #3 $5.30   8.377%   $5.744   $5.74   $5.75   $5.70  
  Purchase #4 $178.25   8.247%   $192.9503   $192.95   $192.95   $193.00  
  Purchase #5 $144.41   8.651%   $156.9029   $156.90   $156.90   $156.90  
  Purchase #6 $152.42   3.842%   $158.276   $158.28   $158.30   $158.30  
  Purchase #7 $136.73   13.331%   $154.9575   $154.96   $154.95   $155.00  
  7 purchase totals = $860.26       $923.3878   $923.39   $923.40   $923.50