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 $59.60   10.107%   $65.6238   $65.62   $65.60   $65.60  
  Purchase #2 $242.64   8.239%   $262.6311   $262.63   $262.65   $262.60  
  Purchase #3 $209.72   5.432%   $221.112   $221.11   $221.10   $221.10  
  Purchase #4 $9.83   6.269%   $10.4462   $10.45   $10.45   $10.40  
  Purchase #5 $67.32   7.454%   $72.338   $72.34   $72.35   $72.30  
  Purchase #6 $226.55   4.150%   $235.9518   $235.95   $235.95   $236.00  
  Purchase #7 $44.67   13.367%   $50.641   $50.64   $50.65   $50.60  
  7 purchase totals = $860.33       $918.7439   $918.74   $918.75   $918.60