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 $213.68   6.128%   $226.7743   $226.77   $226.75   $226.80  
  Purchase #2 $135.96   6.213%   $144.4072   $144.41   $144.40   $144.40  
  Purchase #3 $167.99   4.763%   $175.9914   $175.99   $176.00   $176.00  
  Purchase #4 $161.31   7.401%   $173.2486   $173.25   $173.25   $173.20  
  Purchase #5 $219.59   9.858%   $241.2372   $241.24   $241.25   $241.20  
  Purchase #6 $43.82   6.259%   $46.5627   $46.56   $46.55   $46.60  
  Purchase #7 $51.76   9.703%   $56.7823   $56.78   $56.80   $56.80  
  7 purchase totals = $994.11       $1,065.0037   $1,065.00   $1,065.00   $1,065.00