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 $194.29   5.692%   $205.349   $205.35   $205.35   $205.30  
  Purchase #2 $36.96   10.714%   $40.9199   $40.92   $40.90   $40.90  
  Purchase #3 $38.52   13.271%   $43.632   $43.63   $43.65   $43.60  
  Purchase #4 $148.59   9.839%   $163.2098   $163.21   $163.20   $163.20  
  Purchase #5 $30.95   10.460%   $34.1874   $34.19   $34.20   $34.20  
  Purchase #6 $208.42   12.162%   $233.768   $233.77   $233.75   $233.80  
  Purchase #7 $181.29   8.245%   $196.2374   $196.24   $196.25   $196.20  
  7 purchase totals = $839.02       $917.3035   $917.31   $917.30   $917.20