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 $92.52   3.756%   $95.9951   $96.00   $96.00   $96.00  
  Purchase #2 $82.73   13.239%   $93.6826   $93.68   $93.70   $93.70  
  Purchase #3 $61.52   10.511%   $67.9864   $67.99   $68.00   $68.00  
  Purchase #4 $119.43   4.501%   $124.8055   $124.81   $124.80   $124.80  
  Purchase #5 $77.70   10.623%   $85.9541   $85.95   $85.95   $86.00  
  Purchase #6 $86.74   5.106%   $91.1689   $91.17   $91.15   $91.20  
  Purchase #7 $106.51   3.723%   $110.4754   $110.48   $110.50   $110.50  
  7 purchase totals = $627.15       $670.0680   $670.08   $670.10   $670.20