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 $69.33   6.627%   $73.9245   $73.92   $73.90   $73.90  
  Purchase #2 $160.66   10.107%   $176.8979   $176.90   $176.90   $176.90  
  Purchase #3 $172.90   8.269%   $187.1971   $187.20   $187.20   $187.20  
  Purchase #4 $53.63   4.111%   $55.8347   $55.83   $55.85   $55.80  
  Purchase #5 $228.70   5.582%   $241.466   $241.47   $241.45   $241.50  
  Purchase #6 $199.60   13.377%   $226.3005   $226.30   $226.30   $226.30  
  Purchase #7 $111.35   3.336%   $115.0646   $115.06   $115.05   $115.10  
  7 purchase totals = $996.17       $1,076.6853   $1,076.68   $1,076.65   $1,076.70