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 $208.29   12.157%   $233.6118   $233.61   $233.60   $233.60  
  Purchase #2 $135.80   13.527%   $154.1697   $154.17   $154.15   $154.20  
  Purchase #3 $217.43   5.548%   $229.493   $229.49   $229.50   $229.50  
  Purchase #4 $191.77   5.278%   $201.8916   $201.89   $201.90   $201.90  
  Purchase #5 $218.57   11.725%   $244.1973   $244.20   $244.20   $244.20  
  Purchase #6 $24.70   12.570%   $27.8048   $27.80   $27.80   $27.80  
  Purchase #7 $8.80   8.465%   $9.5449   $9.54   $9.55   $9.50  
  7 purchase totals = $1,005.36       $1,100.7131   $1,100.70   $1,100.70   $1,100.70