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 $185.40   8.626%   $201.3926   $201.39   $201.40   $201.40  
  Purchase #2 $56.58   7.793%   $60.9893   $60.99   $61.00   $61.00  
  Purchase #3 $26.50   3.767%   $27.4983   $27.50   $27.50   $27.50  
  Purchase #4 $220.35   13.389%   $249.8527   $249.85   $249.85   $249.90  
  Purchase #5 $204.55   12.795%   $230.7222   $230.72   $230.70   $230.70  
  Purchase #6 $165.69   5.338%   $174.5345   $174.53   $174.55   $174.50  
  Purchase #7 $63.31   8.379%   $68.6147   $68.61   $68.60   $68.60  
  7 purchase totals = $922.38       $1,013.6043   $1,013.59   $1,013.60   $1,013.60