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 $84.38   3.803%   $87.589   $87.59   $87.60   $87.60  
  Purchase #2 $240.93   3.172%   $248.5723   $248.57   $248.55   $248.60  
  Purchase #3 $46.37   13.475%   $52.6184   $52.62   $52.60   $52.60  
  Purchase #4 $145.89   11.139%   $162.1407   $162.14   $162.15   $162.10  
  Purchase #5 $228.83   10.404%   $252.6375   $252.64   $252.65   $252.60  
  Purchase #6 $95.91   13.643%   $108.995   $109.00   $109.00   $109.00  
  Purchase #7 $12.68   9.283%   $13.8571   $13.86   $13.85   $13.90  
  7 purchase totals = $854.99       $926.4100   $926.42   $926.40   $926.40