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 $61.54   11.307%   $68.4983   $68.50   $68.50   $68.50  
  Purchase #2 $114.75   11.809%   $128.3008   $128.30   $128.30   $128.30  
  Purchase #3 $15.88   6.598%   $16.9278   $16.93   $16.95   $16.90  
  Purchase #4 $230.43   13.225%   $260.9044   $260.90   $260.90   $260.90  
  Purchase #5 $187.66   12.272%   $210.6896   $210.69   $210.70   $210.70  
  Purchase #6 $141.70   7.247%   $151.969   $151.97   $151.95   $152.00  
  Purchase #7 $39.76   11.433%   $44.3058   $44.31   $44.30   $44.30  
  7 purchase totals = $791.72       $881.5957   $881.60   $881.60   $881.60