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 $47.62   4.677%   $49.8472   $49.85   $49.85   $49.80  
  Purchase #2 $233.43   3.533%   $241.6771   $241.68   $241.70   $241.70  
  Purchase #3 $48.82   8.730%   $53.082   $53.08   $53.10   $53.10  
  Purchase #4 $166.62   3.564%   $172.5583   $172.56   $172.55   $172.60  
  Purchase #5 $56.89   9.750%   $62.4368   $62.44   $62.45   $62.40  
  Purchase #6 $170.26   13.328%   $192.9523   $192.95   $192.95   $193.00  
  Purchase #7 $26.27   5.567%   $27.7325   $27.73   $27.75   $27.70  
  7 purchase totals = $749.91       $800.2862   $800.29   $800.35   $800.30