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 $156.97   4.631%   $164.2393   $164.24   $164.25   $164.20  
  Purchase #2 $33.55   8.305%   $36.3363   $36.34   $36.35   $36.30  
  Purchase #3 $218.47   13.394%   $247.7319   $247.73   $247.75   $247.70  
  Purchase #4 $218.86   4.447%   $228.5927   $228.59   $228.60   $228.60  
  Purchase #5 $139.27   13.133%   $157.5603   $157.56   $157.55   $157.60  
  Purchase #6 $158.29   11.182%   $175.99   $175.99   $176.00   $176.00  
  Purchase #7 $168.66   11.778%   $188.5248   $188.52   $188.50   $188.50  
  7 purchase totals = $1,094.07       $1,198.9753   $1,198.97   $1,199.00   $1,198.90