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 $57.97   8.600%   $62.9554   $62.96   $62.95   $63.00  
  Purchase #2 $84.81   13.247%   $96.0448   $96.04   $96.05   $96.00  
  Purchase #3 $66.97   13.401%   $75.9446   $75.94   $75.95   $75.90  
  Purchase #4 $227.99   3.708%   $236.4439   $236.44   $236.45   $236.40  
  Purchase #5 $203.91   9.440%   $223.1591   $223.16   $223.15   $223.20  
  Purchase #6 $41.70   5.191%   $43.8646   $43.86   $43.85   $43.90  
  Purchase #7 $169.42   6.706%   $180.7813   $180.78   $180.80   $180.80  
  7 purchase totals = $852.77       $919.1937   $919.18   $919.20   $919.20