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 $136.34   12.415%   $153.2666   $153.27   $153.25   $153.30  
  Purchase #2 $201.99   11.864%   $225.9541   $225.95   $225.95   $226.00  
  Purchase #3 $77.76   4.693%   $81.4093   $81.41   $81.40   $81.40  
  Purchase #4 $216.49   12.103%   $242.6918   $242.69   $242.70   $242.70  
  Purchase #5 $61.54   8.829%   $66.9734   $66.97   $66.95   $67.00  
  Purchase #6 $157.56   11.338%   $175.4242   $175.42   $175.40   $175.40  
  Purchase #7 $98.40   3.658%   $101.9995   $102.00   $102.00   $102.00  
  7 purchase totals = $950.08       $1,047.7189   $1,047.71   $1,047.65   $1,047.80