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 $63.53   11.670%   $70.944   $70.94   $70.95   $70.90  
  Purchase #2 $249.43   8.222%   $269.9381   $269.94   $269.95   $269.90  
  Purchase #3 $134.27   11.445%   $149.6372   $149.64   $149.65   $149.60  
  Purchase #4 $184.78   5.171%   $194.335   $194.34   $194.35   $194.30  
  Purchase #5 $42.81   9.179%   $46.7395   $46.74   $46.75   $46.70  
  Purchase #6 $126.88   7.379%   $136.2425   $136.24   $136.25   $136.20  
  Purchase #7 $45.60   8.629%   $49.5348   $49.53   $49.55   $49.50  
  7 purchase totals = $847.30       $917.3711   $917.37   $917.45   $917.10