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 $93.92   13.568%   $106.6631   $106.66   $106.65   $106.70  
  Purchase #2 $249.27   13.391%   $282.6497   $282.65   $282.65   $282.60  
  Purchase #3 $246.48   10.117%   $271.4164   $271.42   $271.40   $271.40  
  Purchase #4 $50.66   4.392%   $52.885   $52.89   $52.90   $52.90  
  Purchase #5 $196.62   5.453%   $207.3417   $207.34   $207.35   $207.30  
  Purchase #6 $181.80   3.433%   $188.0412   $188.04   $188.05   $188.00  
  Purchase #7 $68.92   3.734%   $71.4935   $71.49   $71.50   $71.50  
  7 purchase totals = $1,087.67       $1,180.4906   $1,180.49   $1,180.50   $1,180.40