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 $49.58   13.294%   $56.1712   $56.17   $56.15   $56.20  
  Purchase #2 $212.96   9.658%   $233.5277   $233.53   $233.55   $233.50  
  Purchase #3 $221.87   11.773%   $247.9908   $247.99   $248.00   $248.00  
  Purchase #4 $156.73   13.307%   $177.5861   $177.59   $177.60   $177.60  
  Purchase #5 $201.36   4.227%   $209.8715   $209.87   $209.85   $209.90  
  Purchase #6 $164.61   9.169%   $179.7031   $179.70   $179.70   $179.70  
  Purchase #7 $113.78   13.400%   $129.0265   $129.03   $129.05   $129.00  
  7 purchase totals = $1,120.89       $1,233.8769   $1,233.88   $1,233.90   $1,233.90