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 $78.72   8.623%   $85.508   $85.51   $85.50   $85.50  
  Purchase #2 $230.32   10.398%   $254.2687   $254.27   $254.25   $254.30  
  Purchase #3 $111.69   3.417%   $115.5064   $115.51   $115.50   $115.50  
  Purchase #4 $23.39   6.587%   $24.9307   $24.93   $24.95   $24.90  
  Purchase #5 $107.67   10.836%   $119.3371   $119.34   $119.35   $119.30  
  Purchase #6 $236.51   3.567%   $244.9463   $244.95   $244.95   $244.90  
  Purchase #7 $140.53   11.838%   $157.1659   $157.17   $157.15   $157.20  
  7 purchase totals = $928.83       $1,001.6631   $1,001.68   $1,001.65   $1,001.60