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 $163.84   12.152%   $183.7498   $183.75   $183.75   $183.70  
  Purchase #2 $210.65   12.307%   $236.5747   $236.57   $236.55   $236.60  
  Purchase #3 $207.32   12.302%   $232.8245   $232.82   $232.80   $232.80  
  Purchase #4 $101.44   12.633%   $114.2549   $114.25   $114.25   $114.30  
  Purchase #5 $149.45   6.178%   $158.683   $158.68   $158.70   $158.70  
  Purchase #6 $44.52   5.381%   $46.9156   $46.92   $46.90   $46.90  
  Purchase #7 $175.72   5.663%   $185.671   $185.67   $185.65   $185.70  
  7 purchase totals = $1,052.94       $1,158.6735   $1,158.66   $1,158.60   $1,158.70