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 $235.46   13.631%   $267.5556   $267.56   $267.55   $267.60  
  Purchase #2 $107.86   9.343%   $117.9374   $117.94   $117.95   $117.90  
  Purchase #3 $133.80   8.302%   $144.9081   $144.91   $144.90   $144.90  
  Purchase #4 $155.35   13.115%   $175.7242   $175.72   $175.70   $175.70  
  Purchase #5 $28.66   6.428%   $30.5023   $30.50   $30.50   $30.50  
  Purchase #6 $116.69   13.810%   $132.8049   $132.80   $132.80   $132.80  
  Purchase #7 $163.74   12.516%   $184.2337   $184.23   $184.25   $184.20  
  7 purchase totals = $941.56       $1,053.6662   $1,053.66   $1,053.65   $1,053.60