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 $47.33   13.545%   $53.7408   $53.74   $53.75   $53.70  
  Purchase #2 $248.31   6.102%   $263.4619   $263.46   $263.45   $263.50  
  Purchase #3 $234.58   7.363%   $251.8521   $251.85   $251.85   $251.90  
  Purchase #4 $127.88   12.223%   $143.5108   $143.51   $143.50   $143.50  
  Purchase #5 $222.61   9.854%   $244.546   $244.55   $244.55   $244.50  
  Purchase #6 $208.55   6.245%   $221.5739   $221.57   $221.55   $221.60  
  Purchase #7 $58.62   4.197%   $61.0803   $61.08   $61.10   $61.10  
  7 purchase totals = $1,147.88       $1,239.7658   $1,239.76   $1,239.75   $1,239.80