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 $115.97   6.558%   $123.5753   $123.58   $123.60   $123.60  
  Purchase #2 $222.99   10.756%   $246.9748   $246.97   $246.95   $247.00  
  Purchase #3 $164.85   12.592%   $185.6079   $185.61   $185.60   $185.60  
  Purchase #4 $127.36   5.678%   $134.5915   $134.59   $134.60   $134.60  
  Purchase #5 $94.64   5.426%   $99.7752   $99.78   $99.80   $99.80  
  Purchase #6 $111.84   9.660%   $122.6437   $122.64   $122.65   $122.60  
  Purchase #7 $107.93   8.755%   $117.3793   $117.38   $117.40   $117.40  
  7 purchase totals = $945.58       $1,030.5477   $1,030.55   $1,030.60   $1,030.60