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 $76.81   11.670%   $85.7737   $85.77   $85.75   $85.80  
  Purchase #2 $223.33   6.423%   $237.6745   $237.67   $237.65   $237.70  
  Purchase #3 $56.96   6.658%   $60.7524   $60.75   $60.75   $60.80  
  Purchase #4 $57.93   8.329%   $62.755   $62.76   $62.75   $62.80  
  Purchase #5 $181.78   4.219%   $189.4493   $189.45   $189.45   $189.40  
  Purchase #6 $104.96   12.451%   $118.0286   $118.03   $118.05   $118.00  
  Purchase #7 $63.56   12.136%   $71.2736   $71.27   $71.25   $71.30  
  7 purchase totals = $765.33       $825.7071   $825.70   $825.65   $825.80