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 $5.65   6.336%   $6.008   $6.01   $6.00   $6.00  
  Purchase #2 $213.61   4.403%   $223.0152   $223.02   $223.00   $223.00  
  Purchase #3 $62.48   4.568%   $65.3341   $65.33   $65.35   $65.30  
  Purchase #4 $208.88   8.540%   $226.7184   $226.72   $226.70   $226.70  
  Purchase #5 $156.73   5.693%   $165.6526   $165.65   $165.65   $165.70  
  Purchase #6 $95.36   6.445%   $101.506   $101.51   $101.50   $101.50  
  Purchase #7 $226.45   11.346%   $252.143   $252.14   $252.15   $252.10  
  7 purchase totals = $969.16       $1,040.3773   $1,040.38   $1,040.35   $1,040.30