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 $68.87   11.524%   $76.8066   $76.81   $76.80   $76.80  
  Purchase #2 $80.39   4.826%   $84.2696   $84.27   $84.25   $84.30  
  Purchase #3 $68.37   8.214%   $73.9859   $73.99   $74.00   $74.00  
  Purchase #4 $84.79   5.775%   $89.6866   $89.69   $89.70   $89.70  
  Purchase #5 $181.53   13.456%   $205.9567   $205.96   $205.95   $206.00  
  Purchase #6 $98.57   12.369%   $110.7621   $110.76   $110.75   $110.80  
  Purchase #7 $55.29   8.512%   $59.9963   $60.00   $60.00   $60.00  
  7 purchase totals = $637.81       $701.4638   $701.48   $701.45   $701.60