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 $68.91   12.267%   $77.3632   $77.36   $77.35   $77.40  
  Purchase #2 $51.78   8.419%   $56.1394   $56.14   $56.15   $56.10  
  Purchase #3 $233.32   5.824%   $246.9086   $246.91   $246.90   $246.90  
  Purchase #4 $177.65   13.698%   $201.9845   $201.98   $202.00   $202.00  
  Purchase #5 $198.32   3.451%   $205.164   $205.16   $205.15   $205.20  
  Purchase #6 $175.40   11.153%   $194.9624   $194.96   $194.95   $195.00  
  Purchase #7 $82.77   8.125%   $89.4951   $89.50   $89.50   $89.50  
  7 purchase totals = $988.15       $1,072.0172   $1,072.01   $1,072.00   $1,072.10