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 $51.58   13.205%   $58.3911   $58.39   $58.40   $58.40  
  Purchase #2 $248.88   9.544%   $272.6331   $272.63   $272.65   $272.60  
  Purchase #3 $119.33   12.407%   $134.1353   $134.14   $134.15   $134.10  
  Purchase #4 $240.29   3.503%   $248.7074   $248.71   $248.70   $248.70  
  Purchase #5 $107.96   7.131%   $115.6586   $115.66   $115.65   $115.70  
  Purchase #6 $127.80   6.446%   $136.038   $136.04   $136.05   $136.00  
  Purchase #7 $81.35   12.273%   $91.3341   $91.33   $91.35   $91.30  
  7 purchase totals = $977.19       $1,056.8976   $1,056.90   $1,056.95   $1,056.80