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 $247.98   8.637%   $269.398   $269.40   $269.40   $269.40  
  Purchase #2 $149.95   12.403%   $168.5483   $168.55   $168.55   $168.50  
  Purchase #3 $216.25   11.513%   $241.1469   $241.15   $241.15   $241.10  
  Purchase #4 $203.78   11.265%   $226.7358   $226.74   $226.75   $226.70  
  Purchase #5 $155.70   7.250%   $166.9883   $166.99   $167.00   $167.00  
  Purchase #6 $202.99   13.119%   $229.6203   $229.62   $229.60   $229.60  
  Purchase #7 $26.72   13.150%   $30.2337   $30.23   $30.25   $30.20  
  7 purchase totals = $1,203.37       $1,332.6713   $1,332.68   $1,332.70   $1,332.50