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 $83.71   13.123%   $94.6953   $94.70   $94.70   $94.70  
  Purchase #2 $104.77   8.401%   $113.5717   $113.57   $113.55   $113.60  
  Purchase #3 $246.66   13.534%   $280.043   $280.04   $280.05   $280.00  
  Purchase #4 $244.27   8.697%   $265.5142   $265.51   $265.50   $265.50  
  Purchase #5 $202.58   10.124%   $223.0892   $223.09   $223.10   $223.10  
  Purchase #6 $102.66   11.543%   $114.51   $114.51   $114.50   $114.50  
  Purchase #7 $118.54   13.198%   $134.1849   $134.18   $134.20   $134.20  
  7 purchase totals = $1,103.19       $1,225.6083   $1,225.60   $1,225.60   $1,225.60