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 $60.33   12.772%   $68.0353   $68.04   $68.05   $68.00  
  Purchase #2 $246.80   9.366%   $269.9153   $269.92   $269.90   $269.90  
  Purchase #3 $149.26   11.768%   $166.8249   $166.82   $166.80   $166.80  
  Purchase #4 $15.88   4.606%   $16.6114   $16.61   $16.60   $16.60  
  Purchase #5 $181.63   3.769%   $188.4756   $188.48   $188.50   $188.50  
  Purchase #6 $218.34   13.294%   $247.3661   $247.37   $247.35   $247.40  
  Purchase #7 $239.90   12.230%   $269.2398   $269.24   $269.25   $269.20  
  7 purchase totals = $1,112.14       $1,226.4684   $1,226.48   $1,226.45   $1,226.40