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 $56.84   8.183%   $61.4912   $61.49   $61.50   $61.50  
  Purchase #2 $86.77   9.407%   $94.9325   $94.93   $94.95   $94.90  
  Purchase #3 $151.93   3.336%   $156.9984   $157.00   $157.00   $157.00  
  Purchase #4 $101.41   7.238%   $108.7501   $108.75   $108.75   $108.80  
  Purchase #5 $14.34   9.836%   $15.7505   $15.75   $15.75   $15.80  
  Purchase #6 $213.35   3.281%   $220.35   $220.35   $220.35   $220.40  
  Purchase #7 $46.92   9.850%   $51.5416   $51.54   $51.55   $51.50  
  7 purchase totals = $671.56       $709.8143   $709.81   $709.85   $709.90