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 $113.91   3.854%   $118.3001   $118.30   $118.30   $118.30  
  Purchase #2 $97.53   8.119%   $105.4485   $105.45   $105.45   $105.40  
  Purchase #3 $97.54   10.847%   $108.1202   $108.12   $108.10   $108.10  
  Purchase #4 $73.80   13.747%   $83.9453   $83.95   $83.95   $83.90  
  Purchase #5 $248.47   8.784%   $270.2956   $270.30   $270.30   $270.30  
  Purchase #6 $213.47   10.865%   $236.6635   $236.66   $236.65   $236.70  
  Purchase #7 $108.41   12.635%   $122.1076   $122.11   $122.10   $122.10  
  7 purchase totals = $953.13       $1,044.8808   $1,044.89   $1,044.85   $1,044.80