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 $89.46   5.851%   $94.6943   $94.69   $94.70   $94.70  
  Purchase #2 $51.43   10.646%   $56.9052   $56.91   $56.90   $56.90  
  Purchase #3 $62.79   4.519%   $65.6275   $65.63   $65.65   $65.60  
  Purchase #4 $116.90   8.415%   $126.7371   $126.74   $126.75   $126.70  
  Purchase #5 $23.56   13.802%   $26.8118   $26.81   $26.80   $26.80  
  Purchase #6 $127.58   13.401%   $144.677   $144.68   $144.70   $144.70  
  Purchase #7 $189.59   13.322%   $214.8472   $214.85   $214.85   $214.80  
  7 purchase totals = $661.31       $730.3001   $730.31   $730.35   $730.20