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 $169.65   3.776%   $176.056   $176.06   $176.05   $176.10  
  Purchase #2 $153.42   4.598%   $160.4743   $160.47   $160.45   $160.50  
  Purchase #3 $30.74   6.868%   $32.8512   $32.85   $32.85   $32.90  
  Purchase #4 $42.58   3.356%   $44.009   $44.01   $44.00   $44.00  
  Purchase #5 $179.91   3.589%   $186.367   $186.37   $186.35   $186.40  
  Purchase #6 $34.73   4.500%   $36.2929   $36.29   $36.30   $36.30  
  Purchase #7 $51.72   9.478%   $56.622   $56.62   $56.60   $56.60  
  7 purchase totals = $662.75       $692.6724   $692.67   $692.60   $692.80