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 $206.76   8.151%   $223.613   $223.61   $223.60   $223.60  
  Purchase #2 $13.66   4.470%   $14.2706   $14.27   $14.25   $14.30  
  Purchase #3 $160.26   7.259%   $171.8933   $171.89   $171.90   $171.90  
  Purchase #4 $44.46   6.318%   $47.269   $47.27   $47.25   $47.30  
  Purchase #5 $30.87   8.859%   $33.6048   $33.60   $33.60   $33.60  
  Purchase #6 $66.39   11.647%   $74.1224   $74.12   $74.10   $74.10  
  Purchase #7 $207.28   7.603%   $223.0395   $223.04   $223.05   $223.00  
  7 purchase totals = $729.68       $787.8126   $787.80   $787.75   $787.80