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 $32.94   12.174%   $36.9501   $36.95   $36.95   $37.00  
  Purchase #2 $163.74   8.430%   $177.5433   $177.54   $177.55   $177.50  
  Purchase #3 $145.44   13.649%   $165.2911   $165.29   $165.30   $165.30  
  Purchase #4 $134.61   5.124%   $141.5074   $141.51   $141.50   $141.50  
  Purchase #5 $72.41   4.179%   $75.436   $75.44   $75.45   $75.40  
  Purchase #6 $14.56   8.815%   $15.8435   $15.84   $15.85   $15.80  
  Purchase #7 $111.88   13.138%   $126.5788   $126.58   $126.60   $126.60  
  7 purchase totals = $675.58       $739.1502   $739.15   $739.20   $739.10