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 $195.74   6.561%   $208.5825   $208.58   $208.60   $208.60  
  Purchase #2 $119.65   3.815%   $124.2146   $124.21   $124.20   $124.20  
  Purchase #3 $131.84   9.743%   $144.6852   $144.69   $144.70   $144.70  
  Purchase #4 $157.68   12.405%   $177.2402   $177.24   $177.25   $177.20  
  Purchase #5 $229.32   13.586%   $260.4754   $260.48   $260.50   $260.50  
  Purchase #6 $48.40   7.517%   $52.0382   $52.04   $52.05   $52.00  
  Purchase #7 $58.58   8.814%   $63.7432   $63.74   $63.75   $63.70  
  7 purchase totals = $941.21       $1,030.9793   $1,030.98   $1,031.05   $1,030.90