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 $60.47   4.817%   $63.3828   $63.38   $63.40   $63.40  
  Purchase #2 $85.34   10.386%   $94.2034   $94.20   $94.20   $94.20  
  Purchase #3 $7.34   11.107%   $8.1553   $8.16   $8.15   $8.20  
  Purchase #4 $216.79   3.791%   $225.0085   $225.01   $225.00   $225.00  
  Purchase #5 $59.75   3.608%   $61.9058   $61.91   $61.90   $61.90  
  Purchase #6 $50.75   10.545%   $56.1016   $56.10   $56.10   $56.10  
  Purchase #7 $145.88   10.108%   $160.6256   $160.63   $160.65   $160.60  
  7 purchase totals = $626.32       $669.3830   $669.39   $669.40   $669.40