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 $227.86   8.217%   $246.5833   $246.58   $246.60   $246.60  
  Purchase #2 $50.92   3.747%   $52.828   $52.83   $52.85   $52.80  
  Purchase #3 $178.81   11.549%   $199.4608   $199.46   $199.45   $199.50  
  Purchase #4 $126.84   6.849%   $135.5273   $135.53   $135.55   $135.50  
  Purchase #5 $93.93   3.787%   $97.4871   $97.49   $97.50   $97.50  
  Purchase #6 $179.60   8.704%   $195.2324   $195.23   $195.25   $195.20  
  Purchase #7 $124.46   7.397%   $133.6663   $133.67   $133.65   $133.70  
  7 purchase totals = $982.42       $1,060.7852   $1,060.79   $1,060.85   $1,060.80