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 $34.96   3.457%   $36.1686   $36.17   $36.15   $36.20  
  Purchase #2 $83.83   11.144%   $93.172   $93.17   $93.15   $93.20  
  Purchase #3 $177.37   4.852%   $185.976   $185.98   $186.00   $186.00  
  Purchase #4 $25.33   3.451%   $26.2041   $26.20   $26.20   $26.20  
  Purchase #5 $156.31   13.144%   $176.8554   $176.86   $176.85   $176.90  
  Purchase #6 $228.82   12.132%   $256.5804   $256.58   $256.60   $256.60  
  Purchase #7 $147.31   9.464%   $161.2514   $161.25   $161.25   $161.30  
  7 purchase totals = $853.93       $936.2079   $936.21   $936.20   $936.40