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 $248.64   5.598%   $262.5589   $262.56   $262.55   $262.60  
  Purchase #2 $83.47   13.594%   $94.8169   $94.82   $94.80   $94.80  
  Purchase #3 $119.32   4.439%   $124.6166   $124.62   $124.60   $124.60  
  Purchase #4 $247.60   10.455%   $273.4866   $273.49   $273.50   $273.50  
  Purchase #5 $150.43   6.621%   $160.39   $160.39   $160.40   $160.40  
  Purchase #6 $40.44   10.487%   $44.6809   $44.68   $44.70   $44.70  
  Purchase #7 $181.36   3.536%   $187.7729   $187.77   $187.75   $187.80  
  7 purchase totals = $1,071.26       $1,148.3228   $1,148.33   $1,148.30   $1,148.40