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 $207.86   11.769%   $232.323   $232.32   $232.30   $232.30  
  Purchase #2 $213.37   12.601%   $240.2568   $240.26   $240.25   $240.30  
  Purchase #3 $64.27   5.635%   $67.8916   $67.89   $67.90   $67.90  
  Purchase #4 $120.84   5.115%   $127.021   $127.02   $127.00   $127.00  
  Purchase #5 $25.37   4.491%   $26.5094   $26.51   $26.50   $26.50  
  Purchase #6 $7.61   8.230%   $8.2363   $8.24   $8.25   $8.20  
  Purchase #7 $196.42   9.643%   $215.3608   $215.36   $215.35   $215.40  
  7 purchase totals = $835.74       $917.5989   $917.60   $917.55   $917.60