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 $246.37   11.586%   $274.9144   $274.91   $274.90   $274.90  
  Purchase #2 $104.35   3.208%   $107.6975   $107.70   $107.70   $107.70  
  Purchase #3 $85.55   8.489%   $92.8123   $92.81   $92.80   $92.80  
  Purchase #4 $220.55   4.466%   $230.3998   $230.40   $230.40   $230.40  
  Purchase #5 $13.74   6.166%   $14.5872   $14.59   $14.60   $14.60  
  Purchase #6 $217.54   8.641%   $236.3376   $236.34   $236.35   $236.30  
  Purchase #7 $136.46   9.202%   $149.017   $149.02   $149.00   $149.00  
  7 purchase totals = $1,024.56       $1,105.7658   $1,105.77   $1,105.75   $1,105.70