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 $228.69   6.153%   $242.7613   $242.76   $242.75   $242.80  
  Purchase #2 $209.72   8.303%   $227.1331   $227.13   $227.15   $227.10  
  Purchase #3 $217.77   13.698%   $247.6001   $247.60   $247.60   $247.60  
  Purchase #4 $208.79   7.742%   $224.9545   $224.95   $224.95   $225.00  
  Purchase #5 $176.55   13.245%   $199.934   $199.93   $199.95   $199.90  
  Purchase #6 $148.37   5.274%   $156.195   $156.20   $156.20   $156.20  
  Purchase #7 $161.84   3.736%   $167.8863   $167.89   $167.90   $167.90  
  7 purchase totals = $1,351.73       $1,466.4643   $1,466.46   $1,466.50   $1,466.50