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 $74.50   13.151%   $84.2975   $84.30   $84.30   $84.30  
  Purchase #2 $119.27   3.868%   $123.8834   $123.88   $123.90   $123.90  
  Purchase #3 $207.33   3.403%   $214.3854   $214.39   $214.40   $214.40  
  Purchase #4 $155.32   9.432%   $169.9698   $169.97   $169.95   $170.00  
  Purchase #5 $35.60   13.688%   $40.4729   $40.47   $40.45   $40.50  
  Purchase #6 $134.88   8.653%   $146.5512   $146.55   $146.55   $146.60  
  Purchase #7 $219.43   12.323%   $246.4704   $246.47   $246.45   $246.50  
  7 purchase totals = $946.33       $1,026.0306   $1,026.03   $1,026.00   $1,026.20