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 $161.33   13.819%   $183.6242   $183.62   $183.60   $183.60  
  Purchase #2 $214.42   3.502%   $221.929   $221.93   $221.95   $221.90  
  Purchase #3 $84.46   12.487%   $95.0065   $95.01   $95.00   $95.00  
  Purchase #4 $5.67   6.659%   $6.0476   $6.05   $6.05   $6.00  
  Purchase #5 $91.80   7.562%   $98.7419   $98.74   $98.75   $98.70  
  Purchase #6 $156.48   7.716%   $168.554   $168.55   $168.55   $168.60  
  Purchase #7 $243.85   10.326%   $269.03   $269.03   $269.05   $269.00  
  7 purchase totals = $958.01       $1,042.9332   $1,042.93   $1,042.95   $1,042.80