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 $76.54   12.153%   $85.8419   $85.84   $85.85   $85.80  
  Purchase #2 $69.81   3.173%   $72.0251   $72.03   $72.05   $72.00  
  Purchase #3 $72.77   10.239%   $80.2209   $80.22   $80.20   $80.20  
  Purchase #4 $181.84   7.693%   $195.829   $195.83   $195.85   $195.80  
  Purchase #5 $57.38   8.692%   $62.3675   $62.37   $62.35   $62.40  
  Purchase #6 $174.49   11.144%   $193.9352   $193.94   $193.95   $193.90  
  Purchase #7 $192.81   10.373%   $212.8102   $212.81   $212.80   $212.80  
  7 purchase totals = $825.64       $903.0298   $903.04   $903.05   $902.90