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 $67.85   4.724%   $71.0552   $71.06   $71.05   $71.10  
  Purchase #2 $136.73   3.649%   $141.7193   $141.72   $141.70   $141.70  
  Purchase #3 $210.27   8.523%   $228.1913   $228.19   $228.20   $228.20  
  Purchase #4 $52.62   3.485%   $54.4538   $54.45   $54.45   $54.50  
  Purchase #5 $236.64   9.587%   $259.3267   $259.33   $259.35   $259.30  
  Purchase #6 $166.30   6.685%   $177.4172   $177.42   $177.40   $177.40  
  Purchase #7 $85.80   10.106%   $94.4709   $94.47   $94.45   $94.50  
  7 purchase totals = $956.21       $1,026.6344   $1,026.64   $1,026.60   $1,026.70