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 $198.78   9.858%   $218.3757   $218.38   $218.40   $218.40  
  Purchase #2 $240.64   5.319%   $253.4396   $253.44   $253.45   $253.40  
  Purchase #3 $199.47   3.816%   $207.0818   $207.08   $207.10   $207.10  
  Purchase #4 $18.82   10.798%   $20.8522   $20.85   $20.85   $20.90  
  Purchase #5 $36.68   8.169%   $39.6764   $39.68   $39.70   $39.70  
  Purchase #6 $147.58   12.638%   $166.2312   $166.23   $166.25   $166.20  
  Purchase #7 $142.99   11.132%   $158.9076   $158.91   $158.90   $158.90  
  7 purchase totals = $984.96       $1,064.5645   $1,064.57   $1,064.65   $1,064.60