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 $224.58   9.647%   $246.2452   $246.25   $246.25   $246.20  
  Purchase #2 $184.80   10.325%   $203.8806   $203.88   $203.90   $203.90  
  Purchase #3 $50.95   8.105%   $55.0795   $55.08   $55.10   $55.10  
  Purchase #4 $232.62   11.441%   $259.2341   $259.23   $259.25   $259.20  
  Purchase #5 $13.44   3.473%   $13.9068   $13.91   $13.90   $13.90  
  Purchase #6 $189.55   3.819%   $196.7889   $196.79   $196.80   $196.80  
  Purchase #7 $147.38   9.151%   $160.8667   $160.87   $160.85   $160.90  
  7 purchase totals = $1,043.32       $1,136.0018   $1,136.01   $1,136.05   $1,136.00