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 $141.76   11.582%   $158.1786   $158.18   $158.20   $158.20  
  Purchase #2 $126.95   13.594%   $144.2076   $144.21   $144.20   $144.20  
  Purchase #3 $95.86   7.150%   $102.714   $102.71   $102.70   $102.70  
  Purchase #4 $248.96   12.784%   $280.787   $280.79   $280.80   $280.80  
  Purchase #5 $106.71   8.352%   $115.6224   $115.62   $115.60   $115.60  
  Purchase #6 $51.43   9.180%   $56.1513   $56.15   $56.15   $56.20  
  Purchase #7 $226.44   6.807%   $241.8538   $241.85   $241.85   $241.90  
  7 purchase totals = $998.11       $1,099.5147   $1,099.51   $1,099.50   $1,099.60