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 $197.50   8.660%   $214.6035   $214.60   $214.60   $214.60  
  Purchase #2 $98.58   8.512%   $106.9711   $106.97   $106.95   $107.00  
  Purchase #3 $26.71   10.507%   $29.5164   $29.52   $29.50   $29.50  
  Purchase #4 $200.60   6.373%   $213.3842   $213.38   $213.40   $213.40  
  Purchase #5 $250.54   13.261%   $283.7641   $283.76   $283.75   $283.80  
  Purchase #6 $42.58   7.737%   $45.8744   $45.87   $45.85   $45.90  
  Purchase #7 $127.62   13.746%   $145.1626   $145.16   $145.15   $145.20  
  7 purchase totals = $944.13       $1,039.2763   $1,039.26   $1,039.20   $1,039.40