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 $84.52   9.835%   $92.8325   $92.83   $92.85   $92.80  
  Purchase #2 $132.44   8.617%   $143.8524   $143.85   $143.85   $143.90  
  Purchase #3 $54.56   10.291%   $60.1748   $60.17   $60.15   $60.20  
  Purchase #4 $202.61   5.779%   $214.3188   $214.32   $214.30   $214.30  
  Purchase #5 $224.83   6.641%   $239.761   $239.76   $239.75   $239.80  
  Purchase #6 $85.46   6.388%   $90.9192   $90.92   $90.90   $90.90  
  Purchase #7 $233.55   5.536%   $246.4793   $246.48   $246.50   $246.50  
  7 purchase totals = $1,017.97       $1,088.3380   $1,088.33   $1,088.30   $1,088.40