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 $49.39   8.705%   $53.6894   $53.69   $53.70   $53.70  
  Purchase #2 $151.28   10.183%   $166.6848   $166.68   $166.70   $166.70  
  Purchase #3 $134.61   5.576%   $142.1159   $142.12   $142.10   $142.10  
  Purchase #4 $217.73   9.139%   $237.6283   $237.63   $237.65   $237.60  
  Purchase #5 $42.95   7.144%   $46.0183   $46.02   $46.00   $46.00  
  Purchase #6 $161.66   9.296%   $176.6879   $176.69   $176.70   $176.70  
  Purchase #7 $85.75   13.355%   $97.2019   $97.20   $97.20   $97.20  
  7 purchase totals = $843.37       $920.0265   $920.03   $920.05   $920.00