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 $66.89   12.471%   $75.2319   $75.23   $75.25   $75.20  
  Purchase #2 $173.70   13.198%   $196.6249   $196.62   $196.60   $196.60  
  Purchase #3 $15.61   10.530%   $17.2537   $17.25   $17.25   $17.30  
  Purchase #4 $115.46   10.815%   $127.947   $127.95   $127.95   $127.90  
  Purchase #5 $238.95   5.683%   $252.5295   $252.53   $252.55   $252.50  
  Purchase #6 $195.82   4.592%   $204.8121   $204.81   $204.80   $204.80  
  Purchase #7 $28.77   9.385%   $31.4701   $31.47   $31.45   $31.50  
  7 purchase totals = $835.20       $905.8692   $905.86   $905.85   $905.80