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 $86.64   10.182%   $95.4617   $95.46   $95.45   $95.50  
  Purchase #2 $114.66   9.234%   $125.2477   $125.25   $125.25   $125.20  
  Purchase #3 $27.93   6.487%   $29.7418   $29.74   $29.75   $29.70  
  Purchase #4 $134.28   11.288%   $149.4375   $149.44   $149.45   $149.40  
  Purchase #5 $210.35   3.131%   $216.9361   $216.94   $216.95   $216.90  
  Purchase #6 $39.77   8.205%   $43.0331   $43.03   $43.05   $43.00  
  Purchase #7 $22.53   9.773%   $24.7319   $24.73   $24.75   $24.70  
  7 purchase totals = $636.16       $684.5898   $684.59   $684.65   $684.40