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 $247.54   8.247%   $267.9546   $267.95   $267.95   $268.00  
  Purchase #2 $122.89   3.632%   $127.3534   $127.35   $127.35   $127.40  
  Purchase #3 $245.88   4.261%   $256.3569   $256.36   $256.35   $256.40  
  Purchase #4 $173.53   8.354%   $188.0267   $188.03   $188.05   $188.00  
  Purchase #5 $203.91   4.263%   $212.6027   $212.60   $212.60   $212.60  
  Purchase #6 $82.58   3.201%   $85.2234   $85.22   $85.20   $85.20  
  Purchase #7 $118.36   9.529%   $129.6385   $129.64   $129.65   $129.60  
  7 purchase totals = $1,194.69       $1,267.1562   $1,267.15   $1,267.15   $1,267.20