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 $237.72   12.562%   $267.5824   $267.58   $267.60   $267.60  
  Purchase #2 $166.78   8.482%   $180.9263   $180.93   $180.95   $180.90  
  Purchase #3 $153.62   8.490%   $166.6623   $166.66   $166.65   $166.70  
  Purchase #4 $213.29   6.781%   $227.7532   $227.75   $227.75   $227.80  
  Purchase #5 $171.29   4.818%   $179.5428   $179.54   $179.55   $179.50  
  Purchase #6 $65.62   5.389%   $69.1563   $69.16   $69.15   $69.20  
  Purchase #7 $206.98   12.632%   $233.1257   $233.13   $233.15   $233.10  
  7 purchase totals = $1,215.30       $1,324.7490   $1,324.75   $1,324.80   $1,324.80