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 $181.82   10.543%   $200.9893   $200.99   $201.00   $201.00  
  Purchase #2 $56.91   4.436%   $59.4345   $59.43   $59.45   $59.40  
  Purchase #3 $245.37   7.630%   $264.0917   $264.09   $264.10   $264.10  
  Purchase #4 $202.52   9.253%   $221.2592   $221.26   $221.25   $221.30  
  Purchase #5 $82.36   10.489%   $90.9987   $91.00   $91.00   $91.00  
  Purchase #6 $94.52   11.340%   $105.2386   $105.24   $105.25   $105.20  
  Purchase #7 $21.25   11.661%   $23.728   $23.73   $23.75   $23.70  
  7 purchase totals = $884.75       $965.7400   $965.74   $965.80   $965.70