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 $61.98   13.794%   $70.5295   $70.53   $70.55   $70.50  
  Purchase #2 $52.79   4.601%   $55.2189   $55.22   $55.20   $55.20  
  Purchase #3 $96.48   6.730%   $102.9731   $102.97   $102.95   $103.00  
  Purchase #4 $37.87   5.745%   $40.0456   $40.05   $40.05   $40.00  
  Purchase #5 $201.52   12.325%   $226.3573   $226.36   $226.35   $226.40  
  Purchase #6 $193.48   10.460%   $213.718   $213.72   $213.70   $213.70  
  Purchase #7 $234.65   9.423%   $256.7611   $256.76   $256.75   $256.80  
  7 purchase totals = $878.77       $965.6035   $965.61   $965.55   $965.60