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 $211.79   12.476%   $238.2129   $238.21   $238.20   $238.20  
  Purchase #2 $247.86   8.294%   $268.4175   $268.42   $268.40   $268.40  
  Purchase #3 $97.45   8.576%   $105.8073   $105.81   $105.80   $105.80  
  Purchase #4 $153.90   13.299%   $174.3672   $174.37   $174.35   $174.40  
  Purchase #5 $154.30   11.813%   $172.5275   $172.53   $172.55   $172.50  
  Purchase #6 $227.50   9.464%   $249.0306   $249.03   $249.05   $249.00  
  Purchase #7 $61.63   6.580%   $65.6853   $65.69   $65.70   $65.70  
  7 purchase totals = $1,154.43       $1,274.0483   $1,274.06   $1,274.05   $1,274.00