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 $243.85   9.551%   $267.1401   $267.14   $267.15   $267.10  
  Purchase #2 $58.63   12.537%   $65.9804   $65.98   $66.00   $66.00  
  Purchase #3 $15.32   13.543%   $17.3948   $17.39   $17.40   $17.40  
  Purchase #4 $114.61   7.698%   $123.4327   $123.43   $123.45   $123.40  
  Purchase #5 $176.65   9.140%   $192.7958   $192.80   $192.80   $192.80  
  Purchase #6 $224.59   12.412%   $252.4661   $252.47   $252.45   $252.50  
  Purchase #7 $98.52   7.777%   $106.1819   $106.18   $106.20   $106.20  
  7 purchase totals = $932.17       $1,025.3918   $1,025.39   $1,025.45   $1,025.40