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 $61.99   8.112%   $67.0186   $67.02   $67.00   $67.00  
  Purchase #2 $134.59   3.256%   $138.9723   $138.97   $138.95   $139.00  
  Purchase #3 $194.58   3.487%   $201.365   $201.37   $201.35   $201.40  
  Purchase #4 $115.30   11.494%   $128.5526   $128.55   $128.55   $128.60  
  Purchase #5 $173.28   4.745%   $181.5021   $181.50   $181.50   $181.50  
  Purchase #6 $239.86   3.408%   $248.0344   $248.03   $248.05   $248.00  
  Purchase #7 $224.97   6.865%   $240.4142   $240.41   $240.40   $240.40  
  7 purchase totals = $1,144.57       $1,205.8592   $1,205.85   $1,205.80   $1,205.90