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 $182.82   13.371%   $207.2649   $207.26   $207.25   $207.30  
  Purchase #2 $247.73   11.604%   $276.4766   $276.48   $276.50   $276.50  
  Purchase #3 $21.49   6.693%   $22.9283   $22.93   $22.95   $22.90  
  Purchase #4 $204.99   9.576%   $224.6198   $224.62   $224.60   $224.60  
  Purchase #5 $193.96   11.659%   $216.5738   $216.57   $216.55   $216.60  
  Purchase #6 $220.53   8.420%   $239.0986   $239.10   $239.10   $239.10  
  Purchase #7 $177.58   6.142%   $188.487   $188.49   $188.50   $188.50  
  7 purchase totals = $1,249.10       $1,375.4490   $1,375.45   $1,375.45   $1,375.50