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 $214.60   10.331%   $236.7703   $236.77   $236.75   $236.80  
  Purchase #2 $8.35   5.614%   $8.8188   $8.82   $8.80   $8.80  
  Purchase #3 $145.29   7.850%   $156.6953   $156.70   $156.70   $156.70  
  Purchase #4 $95.81   5.156%   $100.75   $100.75   $100.75   $100.80  
  Purchase #5 $184.65   9.824%   $202.79   $202.79   $202.80   $202.80  
  Purchase #6 $72.46   6.817%   $77.3996   $77.40   $77.40   $77.40  
  Purchase #7 $35.63   9.271%   $38.9333   $38.93   $38.95   $38.90  
  7 purchase totals = $756.79       $822.1573   $822.16   $822.15   $822.20