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 $238.60   11.149%   $265.2015   $265.20   $265.20   $265.20  
  Purchase #2 $44.59   11.854%   $49.8757   $49.88   $49.90   $49.90  
  Purchase #3 $53.36   7.759%   $57.5002   $57.50   $57.50   $57.50  
  Purchase #4 $118.54   7.847%   $127.8418   $127.84   $127.85   $127.80  
  Purchase #5 $132.75   12.398%   $149.2083   $149.21   $149.20   $149.20  
  Purchase #6 $91.88   4.658%   $96.1598   $96.16   $96.15   $96.20  
  Purchase #7 $211.81   11.125%   $235.3739   $235.37   $235.35   $235.40  
  7 purchase totals = $891.53       $981.1612   $981.16   $981.15   $981.20