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 $153.41   12.133%   $172.0232   $172.02   $172.00   $172.00  
  Purchase #2 $9.26   4.494%   $9.6761   $9.68   $9.70   $9.70  
  Purchase #3 $144.59   12.137%   $162.1389   $162.14   $162.15   $162.10  
  Purchase #4 $53.72   5.426%   $56.6348   $56.63   $56.65   $56.60  
  Purchase #5 $185.99   6.440%   $197.9678   $197.97   $197.95   $198.00  
  Purchase #6 $223.75   3.456%   $231.4828   $231.48   $231.50   $231.50  
  Purchase #7 $207.81   11.118%   $230.9143   $230.91   $230.90   $230.90  
  7 purchase totals = $978.53       $1,060.8379   $1,060.83   $1,060.85   $1,060.80