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 $192.94   8.134%   $208.6337   $208.63   $208.65   $208.60  
  Purchase #2 $235.85   11.618%   $263.2511   $263.25   $263.25   $263.30  
  Purchase #3 $12.69   4.840%   $13.3042   $13.30   $13.30   $13.30  
  Purchase #4 $224.44   7.521%   $241.3201   $241.32   $241.30   $241.30  
  Purchase #5 $209.52   9.547%   $229.5229   $229.52   $229.50   $229.50  
  Purchase #6 $220.72   9.220%   $241.0704   $241.07   $241.05   $241.10  
  Purchase #7 $57.26   11.416%   $63.7968   $63.80   $63.80   $63.80  
  7 purchase totals = $1,153.42       $1,260.8992   $1,260.89   $1,260.85   $1,260.90