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 $168.28   6.260%   $178.8143   $178.81   $178.80   $178.80  
  Purchase #2 $200.62   12.130%   $224.9552   $224.96   $224.95   $225.00  
  Purchase #3 $41.82   12.218%   $46.9296   $46.93   $46.95   $46.90  
  Purchase #4 $207.54   8.544%   $225.2722   $225.27   $225.25   $225.30  
  Purchase #5 $229.91   11.513%   $256.3795   $256.38   $256.40   $256.40  
  Purchase #6 $142.68   5.704%   $150.8185   $150.82   $150.80   $150.80  
  Purchase #7 $216.65   6.672%   $231.1049   $231.10   $231.10   $231.10  
  7 purchase totals = $1,207.50       $1,314.2742   $1,314.27   $1,314.25   $1,314.30