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 $94.42   13.633%   $107.2923   $107.29   $107.30   $107.30  
  Purchase #2 $87.81   9.543%   $96.1897   $96.19   $96.20   $96.20  
  Purchase #3 $102.77   9.566%   $112.601   $112.60   $112.60   $112.60  
  Purchase #4 $203.63   5.841%   $215.524   $215.52   $215.50   $215.50  
  Purchase #5 $219.28   6.231%   $232.9433   $232.94   $232.95   $232.90  
  Purchase #6 $192.48   3.179%   $198.5989   $198.60   $198.60   $198.60  
  Purchase #7 $42.68   12.494%   $48.0124   $48.01   $48.00   $48.00  
  7 purchase totals = $943.07       $1,011.1616   $1,011.15   $1,011.15   $1,011.10