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 $248.81   13.434%   $282.2351   $282.24   $282.25   $282.20  
  Purchase #2 $116.85   8.652%   $126.9599   $126.96   $126.95   $127.00  
  Purchase #3 $83.32   12.248%   $93.525   $93.53   $93.55   $93.50  
  Purchase #4 $56.32   13.432%   $63.8849   $63.88   $63.90   $63.90  
  Purchase #5 $131.95   11.443%   $147.049   $147.05   $147.05   $147.00  
  Purchase #6 $101.81   4.271%   $106.1583   $106.16   $106.15   $106.20  
  Purchase #7 $189.75   12.182%   $212.8653   $212.87   $212.85   $212.90  
  7 purchase totals = $928.81       $1,032.6775   $1,032.69   $1,032.70   $1,032.70