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 $89.29   8.146%   $96.5636   $96.56   $96.55   $96.60  
  Purchase #2 $134.88   3.611%   $139.7505   $139.75   $139.75   $139.80  
  Purchase #3 $157.82   9.660%   $173.0654   $173.07   $173.05   $173.10  
  Purchase #4 $14.34   13.406%   $16.2624   $16.26   $16.25   $16.30  
  Purchase #5 $232.33   3.768%   $241.0842   $241.08   $241.10   $241.10  
  Purchase #6 $156.65   6.586%   $166.967   $166.97   $166.95   $167.00  
  Purchase #7 $77.74   4.574%   $81.2958   $81.30   $81.30   $81.30  
  7 purchase totals = $863.05       $914.9889   $914.99   $914.95   $915.20