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 $197.66   13.356%   $224.0595   $224.06   $224.05   $224.10  
  Purchase #2 $189.32   11.454%   $211.0047   $211.00   $211.00   $211.00  
  Purchase #3 $111.56   7.531%   $119.9616   $119.96   $119.95   $120.00  
  Purchase #4 $47.45   8.737%   $51.5957   $51.60   $51.60   $51.60  
  Purchase #5 $237.53   12.665%   $267.6132   $267.61   $267.60   $267.60  
  Purchase #6 $114.27   3.755%   $118.5608   $118.56   $118.55   $118.60  
  Purchase #7 $191.30   9.681%   $209.8198   $209.82   $209.80   $209.80  
  7 purchase totals = $1,089.09       $1,202.6153   $1,202.61   $1,202.55   $1,202.70