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 $76.66   13.160%   $86.7485   $86.75   $86.75   $86.70  
  Purchase #2 $157.49   12.675%   $177.4519   $177.45   $177.45   $177.50  
  Purchase #3 $227.35   9.184%   $248.2298   $248.23   $248.25   $248.20  
  Purchase #4 $195.93   8.773%   $213.1189   $213.12   $213.10   $213.10  
  Purchase #5 $9.55   6.474%   $10.1683   $10.17   $10.15   $10.20  
  Purchase #6 $200.64   11.632%   $223.9784   $223.98   $224.00   $224.00  
  Purchase #7 $112.90   9.155%   $123.236   $123.24   $123.25   $123.20  
  7 purchase totals = $980.52       $1,082.9318   $1,082.94   $1,082.95   $1,082.90