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 $98.25   8.528%   $106.6288   $106.63   $106.65   $106.60  
  Purchase #2 $213.69   7.171%   $229.0137   $229.01   $229.00   $229.00  
  Purchase #3 $96.81   8.151%   $104.701   $104.70   $104.70   $104.70  
  Purchase #4 $238.63   5.148%   $250.9147   $250.91   $250.90   $250.90  
  Purchase #5 $61.55   4.465%   $64.2982   $64.30   $64.30   $64.30  
  Purchase #6 $149.29   8.379%   $161.799   $161.80   $161.80   $161.80  
  Purchase #7 $160.97   7.207%   $172.5711   $172.57   $172.55   $172.60  
  7 purchase totals = $1,019.19       $1,089.9265   $1,089.92   $1,089.90   $1,089.90