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 $185.83   13.589%   $211.0824   $211.08   $211.10   $211.10  
  Purchase #2 $113.87   6.680%   $121.4765   $121.48   $121.50   $121.50  
  Purchase #3 $97.28   6.156%   $103.2686   $103.27   $103.25   $103.30  
  Purchase #4 $48.62   12.618%   $54.7549   $54.75   $54.75   $54.80  
  Purchase #5 $138.93   11.501%   $154.9083   $154.91   $154.90   $154.90  
  Purchase #6 $69.27   5.873%   $73.3382   $73.34   $73.35   $73.30  
  Purchase #7 $143.28   13.572%   $162.726   $162.73   $162.75   $162.70  
  7 purchase totals = $797.08       $881.5549   $881.56   $881.60   $881.60