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 $54.91   11.798%   $61.3883   $61.39   $61.40   $61.40  
  Purchase #2 $154.51   9.847%   $169.7246   $169.72   $169.70   $169.70  
  Purchase #3 $29.59   5.785%   $31.3018   $31.30   $31.30   $31.30  
  Purchase #4 $144.68   12.444%   $162.684   $162.68   $162.70   $162.70  
  Purchase #5 $221.35   8.473%   $240.105   $240.11   $240.10   $240.10  
  Purchase #6 $96.54   12.337%   $108.4501   $108.45   $108.45   $108.50  
  Purchase #7 $183.99   7.612%   $197.9953   $198.00   $198.00   $198.00  
  7 purchase totals = $885.57       $971.6491   $971.65   $971.65   $971.70