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 $96.51   4.824%   $101.1656   $101.17   $101.15   $101.20  
  Purchase #2 $64.73   13.842%   $73.6899   $73.69   $73.70   $73.70  
  Purchase #3 $33.53   9.844%   $36.8307   $36.83   $36.85   $36.80  
  Purchase #4 $184.79   5.240%   $194.473   $194.47   $194.45   $194.50  
  Purchase #5 $53.77   7.836%   $57.9834   $57.98   $58.00   $58.00  
  Purchase #6 $119.72   4.543%   $125.1589   $125.16   $125.15   $125.20  
  Purchase #7 $142.86   13.119%   $161.6018   $161.60   $161.60   $161.60  
  7 purchase totals = $695.91       $750.9033   $750.90   $750.90   $751.00