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 $52.36   13.173%   $59.2574   $59.26   $59.25   $59.30  
  Purchase #2 $70.90   8.430%   $76.8769   $76.88   $76.90   $76.90  
  Purchase #3 $235.26   7.761%   $253.5185   $253.52   $253.50   $253.50  
  Purchase #4 $80.55   7.765%   $86.8047   $86.80   $86.80   $86.80  
  Purchase #5 $22.28   7.705%   $23.9967   $24.00   $24.00   $24.00  
  Purchase #6 $112.88   6.286%   $119.9756   $119.98   $120.00   $120.00  
  Purchase #7 $243.61   13.135%   $275.6082   $275.61   $275.60   $275.60  
  7 purchase totals = $817.84       $896.0380   $896.05   $896.05   $896.10