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 $227.58   6.610%   $242.623   $242.62   $242.60   $242.60  
  Purchase #2 $236.89   13.543%   $268.972   $268.97   $268.95   $269.00  
  Purchase #3 $18.45   11.827%   $20.6321   $20.63   $20.65   $20.60  
  Purchase #4 $148.29   12.394%   $166.6691   $166.67   $166.65   $166.70  
  Purchase #5 $18.47   6.516%   $19.6735   $19.67   $19.65   $19.70  
  Purchase #6 $77.47   13.346%   $87.8091   $87.81   $87.80   $87.80  
  Purchase #7 $174.45   10.372%   $192.544   $192.54   $192.55   $192.50  
  7 purchase totals = $901.60       $998.9228   $998.91   $998.85   $998.90