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 $246.56   10.549%   $272.5696   $272.57   $272.55   $272.60  
  Purchase #2 $224.61   13.130%   $254.1013   $254.10   $254.10   $254.10  
  Purchase #3 $99.31   11.651%   $110.8806   $110.88   $110.90   $110.90  
  Purchase #4 $222.50   13.123%   $251.6987   $251.70   $251.70   $251.70  
  Purchase #5 $166.65   8.224%   $180.3553   $180.36   $180.35   $180.40  
  Purchase #6 $161.36   6.398%   $171.6838   $171.68   $171.70   $171.70  
  Purchase #7 $153.43   8.722%   $166.8122   $166.81   $166.80   $166.80  
  7 purchase totals = $1,274.42       $1,408.1015   $1,408.10   $1,408.10   $1,408.20