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 $16.93   12.460%   $19.0395   $19.04   $19.05   $19.00  
  Purchase #2 $195.96   7.658%   $210.9666   $210.97   $210.95   $211.00  
  Purchase #3 $111.96   4.702%   $117.2244   $117.22   $117.20   $117.20  
  Purchase #4 $53.76   7.371%   $57.7226   $57.72   $57.70   $57.70  
  Purchase #5 $117.80   7.511%   $126.648   $126.65   $126.65   $126.60  
  Purchase #6 $178.88   8.339%   $193.7968   $193.80   $193.80   $193.80  
  Purchase #7 $250.62   6.409%   $266.6822   $266.68   $266.70   $266.70  
  7 purchase totals = $925.91       $992.0801   $992.08   $992.05   $992.00