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 $250.49   5.140%   $263.3652   $263.37   $263.35   $263.40  
  Purchase #2 $49.62   5.576%   $52.3868   $52.39   $52.40   $52.40  
  Purchase #3 $15.57   11.505%   $17.3613   $17.36   $17.35   $17.40  
  Purchase #4 $234.30   5.824%   $247.9456   $247.95   $247.95   $247.90  
  Purchase #5 $60.88   5.587%   $64.2814   $64.28   $64.30   $64.30  
  Purchase #6 $208.99   5.430%   $220.3382   $220.34   $220.35   $220.30  
  Purchase #7 $25.42   8.653%   $27.6196   $27.62   $27.60   $27.60  
  7 purchase totals = $845.27       $893.2981   $893.31   $893.30   $893.30