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 $181.63   10.864%   $201.3623   $201.36   $201.35   $201.40  
  Purchase #2 $49.87   10.145%   $54.9293   $54.93   $54.95   $54.90  
  Purchase #3 $201.55   9.852%   $221.4067   $221.41   $221.40   $221.40  
  Purchase #4 $26.96   6.678%   $28.7604   $28.76   $28.75   $28.80  
  Purchase #5 $56.96   5.770%   $60.2466   $60.25   $60.25   $60.20  
  Purchase #6 $15.80   13.532%   $17.9381   $17.94   $17.95   $17.90  
  Purchase #7 $60.49   8.578%   $65.6788   $65.68   $65.70   $65.70  
  7 purchase totals = $593.26       $650.3222   $650.33   $650.35   $650.30