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 $211.65   7.699%   $227.9449   $227.94   $227.95   $227.90  
  Purchase #2 $176.46   8.296%   $191.0991   $191.10   $191.10   $191.10  
  Purchase #3 $123.53   3.468%   $127.814   $127.81   $127.80   $127.80  
  Purchase #4 $186.61   13.452%   $211.7128   $211.71   $211.70   $211.70  
  Purchase #5 $231.53   4.783%   $242.6041   $242.60   $242.60   $242.60  
  Purchase #6 $29.92   6.815%   $31.959   $31.96   $31.95   $32.00  
  Purchase #7 $206.29   9.861%   $226.6323   $226.63   $226.65   $226.60  
  7 purchase totals = $1,165.99       $1,259.7662   $1,259.75   $1,259.75   $1,259.70