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 $60.87   12.642%   $68.5652   $68.57   $68.55   $68.60  
  Purchase #2 $187.30   8.203%   $202.6642   $202.66   $202.65   $202.70  
  Purchase #3 $46.46   8.258%   $50.2967   $50.30   $50.30   $50.30  
  Purchase #4 $56.61   7.167%   $60.6672   $60.67   $60.65   $60.70  
  Purchase #5 $245.63   7.646%   $264.4109   $264.41   $264.40   $264.40  
  Purchase #6 $55.70   11.450%   $62.0777   $62.08   $62.10   $62.10  
  Purchase #7 $232.76   8.378%   $252.2606   $252.26   $252.25   $252.30  
  7 purchase totals = $885.33       $960.9425   $960.95   $960.90   $961.10