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 $121.52   10.714%   $134.5397   $134.54   $134.55   $134.50  
  Purchase #2 $72.77   9.842%   $79.932   $79.93   $79.95   $79.90  
  Purchase #3 $136.99   5.160%   $144.0587   $144.06   $144.05   $144.10  
  Purchase #4 $173.27   12.842%   $195.5213   $195.52   $195.50   $195.50  
  Purchase #5 $138.96   9.869%   $152.674   $152.67   $152.65   $152.70  
  Purchase #6 $218.46   12.399%   $245.5469   $245.55   $245.55   $245.50  
  Purchase #7 $245.90   11.552%   $274.3064   $274.31   $274.30   $274.30  
  7 purchase totals = $1,107.87       $1,226.5790   $1,226.58   $1,226.55   $1,226.50