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 $208.89   12.659%   $235.3334   $235.33   $235.35   $235.30  
  Purchase #2 $195.76   8.684%   $212.7598   $212.76   $212.75   $212.80  
  Purchase #3 $163.43   8.519%   $177.3526   $177.35   $177.35   $177.40  
  Purchase #4 $222.54   8.201%   $240.7905   $240.79   $240.80   $240.80  
  Purchase #5 $135.36   9.609%   $148.3667   $148.37   $148.35   $148.40  
  Purchase #6 $5.34   7.461%   $5.7384   $5.74   $5.75   $5.70  
  Purchase #7 $210.94   12.762%   $237.8602   $237.86   $237.85   $237.90  
  7 purchase totals = $1,142.26       $1,258.2016   $1,258.20   $1,258.20   $1,258.30