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 $61.92   7.609%   $66.6315   $66.63   $66.65   $66.60  
  Purchase #2 $180.63   4.215%   $188.2436   $188.24   $188.25   $188.20  
  Purchase #3 $228.39   8.709%   $248.2805   $248.28   $248.30   $248.30  
  Purchase #4 $27.82   4.153%   $28.9754   $28.98   $29.00   $29.00  
  Purchase #5 $149.47   7.437%   $160.5861   $160.59   $160.60   $160.60  
  Purchase #6 $243.53   10.835%   $269.9165   $269.92   $269.90   $269.90  
  Purchase #7 $89.92   4.193%   $93.6903   $93.69   $93.70   $93.70  
  7 purchase totals = $981.68       $1,056.3239   $1,056.33   $1,056.40   $1,056.30