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 $247.95   11.153%   $275.6039   $275.60   $275.60   $275.60  
  Purchase #2 $237.72   4.248%   $247.8183   $247.82   $247.80   $247.80  
  Purchase #3 $165.80   4.347%   $173.0073   $173.01   $173.00   $173.00  
  Purchase #4 $57.37   9.822%   $63.0049   $63.00   $63.00   $63.00  
  Purchase #5 $230.60   4.663%   $241.3529   $241.35   $241.35   $241.40  
  Purchase #6 $10.70   5.245%   $11.2612   $11.26   $11.25   $11.30  
  Purchase #7 $236.84   4.675%   $247.9123   $247.91   $247.90   $247.90  
  7 purchase totals = $1,186.98       $1,259.9608   $1,259.95   $1,259.90   $1,260.00