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 $191.98   8.759%   $208.7955   $208.80   $208.80   $208.80  
  Purchase #2 $210.46   8.319%   $227.9682   $227.97   $227.95   $228.00  
  Purchase #3 $40.43   4.295%   $42.1665   $42.17   $42.15   $42.20  
  Purchase #4 $57.66   4.217%   $60.0915   $60.09   $60.10   $60.10  
  Purchase #5 $228.47   5.513%   $241.0656   $241.07   $241.05   $241.10  
  Purchase #6 $249.82   9.154%   $272.6885   $272.69   $272.70   $272.70  
  Purchase #7 $193.92   5.567%   $204.7155   $204.72   $204.70   $204.70  
  7 purchase totals = $1,172.74       $1,257.4913   $1,257.51   $1,257.45   $1,257.60