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 $119.35   10.621%   $132.0262   $132.03   $132.05   $132.00  
  Purchase #2 $227.33   13.388%   $257.7649   $257.76   $257.75   $257.80  
  Purchase #3 $194.89   10.619%   $215.5854   $215.59   $215.60   $215.60  
  Purchase #4 $116.44   3.525%   $120.5445   $120.54   $120.55   $120.50  
  Purchase #5 $59.76   9.134%   $65.2185   $65.22   $65.20   $65.20  
  Purchase #6 $114.75   10.851%   $127.2015   $127.20   $127.20   $127.20  
  Purchase #7 $226.48   4.201%   $235.9944   $235.99   $236.00   $236.00  
  7 purchase totals = $1,059.00       $1,154.3354   $1,154.33   $1,154.35   $1,154.30