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 $59.72   6.634%   $63.6818   $63.68   $63.70   $63.70  
  Purchase #2 $101.97   8.554%   $110.6925   $110.69   $110.70   $110.70  
  Purchase #3 $38.50   10.212%   $42.4316   $42.43   $42.45   $42.40  
  Purchase #4 $108.52   13.305%   $122.9586   $122.96   $122.95   $123.00  
  Purchase #5 $59.52   6.176%   $63.196   $63.20   $63.20   $63.20  
  Purchase #6 $192.26   3.787%   $199.5409   $199.54   $199.55   $199.50  
  Purchase #7 $189.45   4.592%   $198.1495   $198.15   $198.15   $198.10  
  7 purchase totals = $749.94       $800.6509   $800.65   $800.70   $800.60