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 $226.59   12.414%   $254.7189   $254.72   $254.70   $254.70  
  Purchase #2 $237.53   4.688%   $248.6654   $248.67   $248.65   $248.70  
  Purchase #3 $159.58   9.776%   $175.1805   $175.18   $175.20   $175.20  
  Purchase #4 $233.31   9.720%   $255.9877   $255.99   $256.00   $256.00  
  Purchase #5 $108.58   13.265%   $122.9831   $122.98   $123.00   $123.00  
  Purchase #6 $175.92   7.746%   $189.5468   $189.55   $189.55   $189.50  
  Purchase #7 $53.86   10.610%   $59.5745   $59.57   $59.55   $59.60  
  7 purchase totals = $1,195.37       $1,306.6569   $1,306.66   $1,306.65   $1,306.70