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 $63.42   9.717%   $69.5825   $69.58   $69.60   $69.60  
  Purchase #2 $94.34   10.513%   $104.258   $104.26   $104.25   $104.30  
  Purchase #3 $118.97   5.858%   $125.9393   $125.94   $125.95   $125.90  
  Purchase #4 $204.93   10.768%   $226.9969   $227.00   $227.00   $227.00  
  Purchase #5 $30.28   12.480%   $34.0589   $34.06   $34.05   $34.10  
  Purchase #6 $180.73   3.853%   $187.6935   $187.69   $187.70   $187.70  
  Purchase #7 $245.38   13.320%   $278.0646   $278.06   $278.05   $278.10  
  7 purchase totals = $938.05       $1,026.5937   $1,026.59   $1,026.60   $1,026.70