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 $204.95   4.296%   $213.7547   $213.75   $213.75   $213.80  
  Purchase #2 $222.52   9.188%   $242.9651   $242.97   $242.95   $243.00  
  Purchase #3 $30.80   7.310%   $33.0515   $33.05   $33.05   $33.10  
  Purchase #4 $162.45   11.791%   $181.6045   $181.60   $181.60   $181.60  
  Purchase #5 $169.81   12.391%   $190.8512   $190.85   $190.85   $190.90  
  Purchase #6 $96.85   11.539%   $108.0255   $108.03   $108.05   $108.00  
  Purchase #7 $248.40   5.628%   $262.38   $262.38   $262.40   $262.40  
  7 purchase totals = $1,135.78       $1,232.6325   $1,232.63   $1,232.65   $1,232.80