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 $63.95   12.466%   $71.922   $71.92   $71.90   $71.90  
  Purchase #2 $75.55   13.457%   $85.7168   $85.72   $85.70   $85.70  
  Purchase #3 $30.96   11.223%   $34.4346   $34.43   $34.45   $34.40  
  Purchase #4 $164.77   9.735%   $180.8104   $180.81   $180.80   $180.80  
  Purchase #5 $14.89   11.627%   $16.6213   $16.62   $16.60   $16.60  
  Purchase #6 $211.26   5.866%   $223.6525   $223.65   $223.65   $223.70  
  Purchase #7 $145.67   7.267%   $156.2558   $156.26   $156.25   $156.30  
  7 purchase totals = $707.05       $769.4134   $769.41   $769.35   $769.40