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 $84.73   12.590%   $95.3975   $95.40   $95.40   $95.40  
  Purchase #2 $30.52   13.432%   $34.6194   $34.62   $34.60   $34.60  
  Purchase #3 $118.29   4.466%   $123.5728   $123.57   $123.55   $123.60  
  Purchase #4 $207.37   4.474%   $216.6477   $216.65   $216.65   $216.60  
  Purchase #5 $121.99   4.836%   $127.8894   $127.89   $127.90   $127.90  
  Purchase #6 $58.42   10.442%   $64.5202   $64.52   $64.50   $64.50  
  Purchase #7 $24.81   5.679%   $26.219   $26.22   $26.20   $26.20  
  7 purchase totals = $646.13       $688.8660   $688.87   $688.80   $688.80