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 $55.43   9.446%   $60.6659   $60.67   $60.65   $60.70  
  Purchase #2 $235.32   10.342%   $259.6568   $259.66   $259.65   $259.70  
  Purchase #3 $192.53   7.125%   $206.2478   $206.25   $206.25   $206.20  
  Purchase #4 $237.64   10.568%   $262.7538   $262.75   $262.75   $262.80  
  Purchase #5 $68.82   6.357%   $73.1949   $73.19   $73.20   $73.20  
  Purchase #6 $160.32   13.403%   $181.8077   $181.81   $181.80   $181.80  
  Purchase #7 $11.87   5.334%   $12.5031   $12.50   $12.50   $12.50  
  7 purchase totals = $961.93       $1,056.8300   $1,056.83   $1,056.80   $1,056.90