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 $23.44   11.159%   $26.0557   $26.06   $26.05   $26.10  
  Purchase #2 $91.98   6.196%   $97.6791   $97.68   $97.70   $97.70  
  Purchase #3 $66.59   3.659%   $69.0265   $69.03   $69.05   $69.00  
  Purchase #4 $70.76   4.636%   $74.0404   $74.04   $74.05   $74.00  
  Purchase #5 $228.84   10.652%   $253.216   $253.22   $253.20   $253.20  
  Purchase #6 $59.60   4.560%   $62.3178   $62.32   $62.30   $62.30  
  Purchase #7 $72.98   7.868%   $78.7221   $78.72   $78.70   $78.70  
  7 purchase totals = $614.19       $661.0576   $661.07   $661.05   $661.00