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 $56.34   3.274%   $58.1846   $58.18   $58.20   $58.20  
  Purchase #2 $182.41   4.793%   $191.1529   $191.15   $191.15   $191.20  
  Purchase #3 $212.40   6.867%   $226.9855   $226.99   $227.00   $227.00  
  Purchase #4 $77.57   8.131%   $83.8772   $83.88   $83.90   $83.90  
  Purchase #5 $23.28   12.723%   $26.2419   $26.24   $26.25   $26.20  
  Purchase #6 $118.46   7.817%   $127.72   $127.72   $127.70   $127.70  
  Purchase #7 $73.78   7.664%   $79.4345   $79.43   $79.45   $79.40  
  7 purchase totals = $744.24       $793.5966   $793.59   $793.65   $793.60