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 $37.89   13.844%   $43.1355   $43.14   $43.15   $43.10  
  Purchase #2 $178.43   8.718%   $193.9855   $193.99   $194.00   $194.00  
  Purchase #3 $158.98   5.334%   $167.46   $167.46   $167.45   $167.50  
  Purchase #4 $71.57   3.616%   $74.158   $74.16   $74.15   $74.20  
  Purchase #5 $188.29   3.588%   $195.0458   $195.05   $195.05   $195.00  
  Purchase #6 $242.74   9.819%   $266.5746   $266.57   $266.55   $266.60  
  Purchase #7 $241.39   9.836%   $265.1331   $265.13   $265.15   $265.10  
  7 purchase totals = $1,119.29       $1,205.4925   $1,205.50   $1,205.50   $1,205.50