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 $246.51   6.481%   $262.4863   $262.49   $262.50   $262.50  
  Purchase #2 $240.36   11.780%   $268.6744   $268.67   $268.65   $268.70  
  Purchase #3 $147.66   7.154%   $158.2236   $158.22   $158.20   $158.20  
  Purchase #4 $222.59   7.545%   $239.3844   $239.38   $239.40   $239.40  
  Purchase #5 $47.31   13.273%   $53.5895   $53.59   $53.60   $53.60  
  Purchase #6 $48.46   12.536%   $54.5349   $54.53   $54.55   $54.50  
  Purchase #7 $227.60   3.610%   $235.8164   $235.82   $235.80   $235.80  
  7 purchase totals = $1,180.49       $1,272.7095   $1,272.70   $1,272.70   $1,272.70