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 $60.57   5.127%   $63.6754   $63.68   $63.70   $63.70  
  Purchase #2 $188.33   8.394%   $204.1384   $204.14   $204.15   $204.10  
  Purchase #3 $241.31   11.692%   $269.524   $269.52   $269.50   $269.50  
  Purchase #4 $41.63   6.591%   $44.3738   $44.37   $44.35   $44.40  
  Purchase #5 $77.67   4.688%   $81.3112   $81.31   $81.30   $81.30  
  Purchase #6 $139.50   11.340%   $155.3193   $155.32   $155.30   $155.30  
  Purchase #7 $53.96   8.224%   $58.3977   $58.40   $58.40   $58.40  
  7 purchase totals = $802.97       $876.7398   $876.74   $876.70   $876.70