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 $248.74   3.840%   $258.2916   $258.29   $258.30   $258.30  
  Purchase #2 $241.85   6.706%   $258.0685   $258.07   $258.05   $258.10  
  Purchase #3 $10.65   13.421%   $12.0793   $12.08   $12.10   $12.10  
  Purchase #4 $7.85   6.634%   $8.3708   $8.37   $8.35   $8.40  
  Purchase #5 $209.25   9.411%   $228.9425   $228.94   $228.95   $228.90  
  Purchase #6 $104.90   7.213%   $112.4664   $112.47   $112.45   $112.50  
  Purchase #7 $217.38   13.152%   $245.9698   $245.97   $245.95   $246.00  
  7 purchase totals = $1,040.62       $1,124.1889   $1,124.19   $1,124.15   $1,124.30