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 $66.75   5.666%   $70.5321   $70.53   $70.55   $70.50  
  Purchase #2 $221.91   11.295%   $246.9747   $246.97   $246.95   $247.00  
  Purchase #3 $108.28   7.124%   $115.9939   $115.99   $116.00   $116.00  
  Purchase #4 $53.66   10.577%   $59.3356   $59.34   $59.35   $59.30  
  Purchase #5 $153.91   8.139%   $166.4367   $166.44   $166.45   $166.40  
  Purchase #6 $172.72   9.231%   $188.6638   $188.66   $188.65   $188.70  
  Purchase #7 $206.98   4.582%   $216.4638   $216.46   $216.45   $216.50  
  7 purchase totals = $984.21       $1,064.4006   $1,064.39   $1,064.40   $1,064.40