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 $171.44   12.868%   $193.5009   $193.50   $193.50   $193.50  
  Purchase #2 $208.83   6.179%   $221.7336   $221.73   $221.75   $221.70  
  Purchase #3 $105.36   6.630%   $112.3454   $112.35   $112.35   $112.30  
  Purchase #4 $79.29   8.528%   $86.0519   $86.05   $86.05   $86.10  
  Purchase #5 $183.94   9.678%   $201.7417   $201.74   $201.75   $201.70  
  Purchase #6 $180.84   6.379%   $192.3758   $192.38   $192.40   $192.40  
  Purchase #7 $232.93   6.369%   $247.7653   $247.77   $247.75   $247.80  
  7 purchase totals = $1,162.63       $1,255.5146   $1,255.52   $1,255.55   $1,255.50