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 $249.33   3.332%   $257.6377   $257.64   $257.65   $257.60  
  Purchase #2 $110.51   12.755%   $124.6056   $124.61   $124.60   $124.60  
  Purchase #3 $72.84   3.744%   $75.5671   $75.57   $75.55   $75.60  
  Purchase #4 $196.43   11.638%   $219.2905   $219.29   $219.30   $219.30  
  Purchase #5 $58.57   10.242%   $64.5687   $64.57   $64.55   $64.60  
  Purchase #6 $174.70   13.289%   $197.9159   $197.92   $197.90   $197.90  
  Purchase #7 $104.83   13.603%   $119.09   $119.09   $119.10   $119.10  
  7 purchase totals = $967.21       $1,058.6755   $1,058.69   $1,058.65   $1,058.70