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 $65.47   4.383%   $68.3396   $68.34   $68.35   $68.30  
  Purchase #2 $137.35   6.448%   $146.2063   $146.21   $146.20   $146.20  
  Purchase #3 $186.53   7.748%   $200.9823   $200.98   $201.00   $201.00  
  Purchase #4 $57.77   4.317%   $60.2639   $60.26   $60.25   $60.30  
  Purchase #5 $29.44   6.529%   $31.3621   $31.36   $31.35   $31.40  
  Purchase #6 $201.89   3.478%   $208.9117   $208.91   $208.90   $208.90  
  Purchase #7 $139.91   7.537%   $150.455   $150.46   $150.45   $150.50  
  7 purchase totals = $818.36       $866.5209   $866.52   $866.50   $866.60