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 $95.77   5.561%   $101.0958   $101.10   $101.10   $101.10  
  Purchase #2 $242.58   11.145%   $269.6155   $269.62   $269.60   $269.60  
  Purchase #3 $54.81   3.770%   $56.8763   $56.88   $56.90   $56.90  
  Purchase #4 $189.80   8.565%   $206.0564   $206.06   $206.05   $206.10  
  Purchase #5 $10.70   8.342%   $11.5926   $11.59   $11.60   $11.60  
  Purchase #6 $240.96   10.672%   $266.6753   $266.68   $266.70   $266.70  
  Purchase #7 $161.47   11.788%   $180.5041   $180.50   $180.50   $180.50  
  7 purchase totals = $996.09       $1,092.4160   $1,092.43   $1,092.45   $1,092.50