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 $89.94   5.311%   $94.7167   $94.72   $94.70   $94.70  
  Purchase #2 $66.78   10.557%   $73.83   $73.83   $73.85   $73.80  
  Purchase #3 $178.25   8.573%   $193.5314   $193.53   $193.55   $193.50  
  Purchase #4 $38.97   11.421%   $43.4208   $43.42   $43.40   $43.40  
  Purchase #5 $217.31   8.545%   $235.8791   $235.88   $235.90   $235.90  
  Purchase #6 $142.45   9.678%   $156.2363   $156.24   $156.25   $156.20  
  Purchase #7 $60.81   5.490%   $64.1485   $64.15   $64.15   $64.10  
  7 purchase totals = $794.51       $861.7628   $861.77   $861.80   $861.60