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 $186.30   8.467%   $202.074   $202.07   $202.05   $202.10  
  Purchase #2 $97.92   7.284%   $105.0525   $105.05   $105.05   $105.10  
  Purchase #3 $108.38   9.493%   $118.6685   $118.67   $118.65   $118.70  
  Purchase #4 $120.55   10.798%   $133.567   $133.57   $133.55   $133.60  
  Purchase #5 $54.75   11.860%   $61.2434   $61.24   $61.25   $61.20  
  Purchase #6 $108.98   6.135%   $115.6659   $115.67   $115.65   $115.70  
  Purchase #7 $86.57   4.440%   $90.4137   $90.41   $90.40   $90.40  
  7 purchase totals = $763.45       $826.6850   $826.68   $826.60   $826.80