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   11.521%   $276.5163   $276.52   $276.50   $276.50  
  Purchase #2 $45.63   9.280%   $49.8645   $49.86   $49.85   $49.90  
  Purchase #3 $112.60   6.438%   $119.8492   $119.85   $119.85   $119.80  
  Purchase #4 $9.57   4.275%   $9.9791   $9.98   $10.00   $10.00  
  Purchase #5 $228.65   11.685%   $255.3678   $255.37   $255.35   $255.40  
  Purchase #6 $16.40   3.268%   $16.936   $16.94   $16.95   $16.90  
  Purchase #7 $92.56   6.258%   $98.3524   $98.35   $98.35   $98.40  
  7 purchase totals = $753.36       $826.8653   $826.87   $826.85   $826.90