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 $55.28   11.238%   $61.4924   $61.49   $61.50   $61.50  
  Purchase #2 $135.28   5.212%   $142.3308   $142.33   $142.35   $142.30  
  Purchase #3 $140.53   11.534%   $156.7387   $156.74   $156.75   $156.70  
  Purchase #4 $11.85   5.789%   $12.536   $12.54   $12.55   $12.50  
  Purchase #5 $195.43   7.619%   $210.3198   $210.32   $210.30   $210.30  
  Purchase #6 $233.54   12.759%   $263.3374   $263.34   $263.35   $263.30  
  Purchase #7 $119.66   7.284%   $128.376   $128.38   $128.40   $128.40  
  7 purchase totals = $891.57       $975.1311   $975.14   $975.20   $975.00