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 $238.82   12.181%   $267.9107   $267.91   $267.90   $267.90  
  Purchase #2 $177.73   13.181%   $201.1566   $201.16   $201.15   $201.20  
  Purchase #3 $70.48   7.201%   $75.5553   $75.56   $75.55   $75.60  
  Purchase #4 $147.31   9.834%   $161.7965   $161.80   $161.80   $161.80  
  Purchase #5 $72.42   3.296%   $74.807   $74.81   $74.80   $74.80  
  Purchase #6 $52.72   6.610%   $56.2048   $56.20   $56.20   $56.20  
  Purchase #7 $110.34   4.253%   $115.0328   $115.03   $115.05   $115.00  
  7 purchase totals = $869.82       $952.4637   $952.47   $952.45   $952.50