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 $108.42   10.461%   $119.7618   $119.76   $119.75   $119.80  
  Purchase #2 $215.84   9.119%   $235.5224   $235.52   $235.50   $235.50  
  Purchase #3 $9.55   5.453%   $10.0708   $10.07   $10.05   $10.10  
  Purchase #4 $26.26   12.192%   $29.4616   $29.46   $29.45   $29.50  
  Purchase #5 $99.90   10.697%   $110.5863   $110.59   $110.60   $110.60  
  Purchase #6 $249.73   3.442%   $258.3257   $258.33   $258.35   $258.30  
  Purchase #7 $29.95   10.365%   $33.0543   $33.05   $33.05   $33.10  
  7 purchase totals = $739.65       $796.7829   $796.78   $796.75   $796.90