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 $201.39   6.273%   $214.0232   $214.02   $214.00   $214.00  
  Purchase #2 $55.34   10.861%   $61.3505   $61.35   $61.35   $61.40  
  Purchase #3 $240.57   3.418%   $248.7927   $248.79   $248.80   $248.80  
  Purchase #4 $86.73   10.657%   $95.9728   $95.97   $95.95   $96.00  
  Purchase #5 $187.29   13.178%   $211.9711   $211.97   $211.95   $212.00  
  Purchase #6 $216.73   3.690%   $224.7273   $224.73   $224.75   $224.70  
  Purchase #7 $136.72   3.467%   $141.4601   $141.46   $141.45   $141.50  
  7 purchase totals = $1,124.77       $1,198.2977   $1,198.29   $1,198.25   $1,198.40