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 $240.93   10.529%   $266.2975   $266.30   $266.30   $266.30  
  Purchase #2 $227.39   6.347%   $241.8224   $241.82   $241.80   $241.80  
  Purchase #3 $117.70   8.370%   $127.5515   $127.55   $127.55   $127.60  
  Purchase #4 $26.37   6.590%   $28.1078   $28.11   $28.10   $28.10  
  Purchase #5 $64.69   10.495%   $71.4792   $71.48   $71.50   $71.50  
  Purchase #6 $209.30   6.643%   $223.2038   $223.20   $223.20   $223.20  
  Purchase #7 $196.85   4.185%   $205.0882   $205.09   $205.10   $205.10  
  7 purchase totals = $1,083.23       $1,163.5504   $1,163.55   $1,163.55   $1,163.60