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 $98.43   4.725%   $103.0808   $103.08   $103.10   $103.10  
  Purchase #2 $201.86   8.806%   $219.6358   $219.64   $219.65   $219.60  
  Purchase #3 $44.27   9.801%   $48.6089   $48.61   $48.60   $48.60  
  Purchase #4 $52.33   9.124%   $57.1046   $57.10   $57.10   $57.10  
  Purchase #5 $17.42   3.589%   $18.0452   $18.05   $18.05   $18.00  
  Purchase #6 $114.49   9.812%   $125.7238   $125.72   $125.70   $125.70  
  Purchase #7 $133.62   8.700%   $145.2449   $145.24   $145.25   $145.20  
  7 purchase totals = $662.42       $717.4440   $717.44   $717.45   $717.30