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 $144.38   5.411%   $152.1924   $152.19   $152.20   $152.20  
  Purchase #2 $245.64   11.841%   $274.7262   $274.73   $274.75   $274.70  
  Purchase #3 $155.33   9.535%   $170.1407   $170.14   $170.15   $170.10  
  Purchase #4 $53.37   9.107%   $58.2304   $58.23   $58.25   $58.20  
  Purchase #5 $96.81   9.695%   $106.1957   $106.20   $106.20   $106.20  
  Purchase #6 $169.59   3.435%   $175.4154   $175.42   $175.40   $175.40  
  Purchase #7 $18.70   13.516%   $21.2275   $21.23   $21.25   $21.20  
  7 purchase totals = $883.82       $958.1283   $958.14   $958.20   $958.00