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 $58.38   12.529%   $65.6944   $65.69   $65.70   $65.70  
  Purchase #2 $8.75   5.782%   $9.2559   $9.26   $9.25   $9.30  
  Purchase #3 $232.66   7.669%   $250.5027   $250.50   $250.50   $250.50  
  Purchase #4 $219.52   6.541%   $233.8788   $233.88   $233.90   $233.90  
  Purchase #5 $92.38   6.828%   $98.6877   $98.69   $98.70   $98.70  
  Purchase #6 $90.83   8.595%   $98.6368   $98.64   $98.65   $98.60  
  Purchase #7 $217.69   12.374%   $244.627   $244.63   $244.65   $244.60  
  7 purchase totals = $920.21       $1,001.2833   $1,001.29   $1,001.35   $1,001.30