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 $92.97   5.852%   $98.4106   $98.41   $98.40   $98.40  
  Purchase #2 $190.33   9.125%   $207.6976   $207.70   $207.70   $207.70  
  Purchase #3 $199.89   8.413%   $216.7067   $216.71   $216.70   $216.70  
  Purchase #4 $219.83   4.348%   $229.3882   $229.39   $229.40   $229.40  
  Purchase #5 $35.72   5.392%   $37.646   $37.65   $37.65   $37.60  
  Purchase #6 $246.25   6.675%   $262.6872   $262.69   $262.70   $262.70  
  Purchase #7 $135.80   13.457%   $154.0746   $154.07   $154.05   $154.10  
  7 purchase totals = $1,120.79       $1,206.6109   $1,206.62   $1,206.60   $1,206.60