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 $64.83   7.825%   $69.9029   $69.90   $69.90   $69.90  
  Purchase #2 $73.42   5.445%   $77.4177   $77.42   $77.40   $77.40  
  Purchase #3 $25.97   3.423%   $26.859   $26.86   $26.85   $26.90  
  Purchase #4 $168.81   9.413%   $184.7001   $184.70   $184.70   $184.70  
  Purchase #5 $244.50   8.484%   $265.2434   $265.24   $265.25   $265.20  
  Purchase #6 $147.53   4.342%   $153.9358   $153.94   $153.95   $153.90  
  Purchase #7 $217.92   9.613%   $238.8686   $238.87   $238.85   $238.90  
  7 purchase totals = $942.98       $1,016.9275   $1,016.93   $1,016.90   $1,016.90