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 $52.61   7.818%   $56.723   $56.72   $56.70   $56.70  
  Purchase #2 $101.89   11.591%   $113.7001   $113.70   $113.70   $113.70  
  Purchase #3 $196.31   8.264%   $212.5331   $212.53   $212.55   $212.50  
  Purchase #4 $198.56   6.213%   $210.8965   $210.90   $210.90   $210.90  
  Purchase #5 $153.75   13.579%   $174.6277   $174.63   $174.65   $174.60  
  Purchase #6 $166.99   3.834%   $173.3924   $173.39   $173.40   $173.40  
  Purchase #7 $91.70   8.791%   $99.7613   $99.76   $99.75   $99.80  
  7 purchase totals = $961.81       $1,041.6341   $1,041.63   $1,041.65   $1,041.60