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 $62.83   4.212%   $65.4764   $65.48   $65.50   $65.50  
  Purchase #2 $241.39   7.289%   $258.9849   $258.98   $259.00   $259.00  
  Purchase #3 $198.33   6.249%   $210.7236   $210.72   $210.70   $210.70  
  Purchase #4 $54.39   3.626%   $56.3622   $56.36   $56.35   $56.40  
  Purchase #5 $61.98   10.633%   $68.5703   $68.57   $68.55   $68.60  
  Purchase #6 $59.48   5.234%   $62.5932   $62.59   $62.60   $62.60  
  Purchase #7 $225.52   10.835%   $249.9551   $249.96   $249.95   $250.00  
  7 purchase totals = $903.92       $972.6657   $972.66   $972.65   $972.80