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 $6.50   9.640%   $7.1266   $7.13   $7.15   $7.10  
  Purchase #2 $166.69   9.716%   $182.8856   $182.89   $182.90   $182.90  
  Purchase #3 $220.81   13.526%   $250.6768   $250.68   $250.70   $250.70  
  Purchase #4 $92.44   6.460%   $98.4116   $98.41   $98.40   $98.40  
  Purchase #5 $10.90   8.145%   $11.7878   $11.79   $11.80   $11.80  
  Purchase #6 $113.84   5.561%   $120.1706   $120.17   $120.15   $120.20  
  Purchase #7 $73.77   9.225%   $80.5753   $80.58   $80.60   $80.60  
  7 purchase totals = $684.95       $751.6343   $751.65   $751.70   $751.70