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 $232.63   12.604%   $261.9507   $261.95   $261.95   $262.00  
  Purchase #2 $216.31   8.333%   $234.3351   $234.34   $234.35   $234.30  
  Purchase #3 $199.55   7.516%   $214.5482   $214.55   $214.55   $214.50  
  Purchase #4 $65.32   5.102%   $68.6526   $68.65   $68.65   $68.70  
  Purchase #5 $91.82   12.863%   $103.6308   $103.63   $103.65   $103.60  
  Purchase #6 $37.94   8.745%   $41.2579   $41.26   $41.25   $41.30  
  Purchase #7 $95.99   11.263%   $106.8014   $106.80   $106.80   $106.80  
  7 purchase totals = $939.56       $1,031.1767   $1,031.18   $1,031.20   $1,031.20